Prognostic value of micrometastases in sentinel lymph nodes of patients with breast carcinoma: a cohort study

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1 Annals of Oncology 20: 41 48, 2009 doi: /annonc/mdn535 Published online 24 July 2008 Prognostic value of micrometastases in sentinel lymph nodes of patients with breast carcinoma: a cohort study P. D. Gobardhan 4, S. G. Elias 1, E. V. E. Madsen 4, V. Bongers 2, H. J. M. Ruitenberg 3, C. I. Perre 4 & T. van Dalen 4 * 1 Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht; 2 Department of Nuclear Medicine, Diakonessenhuis Utrecht; 3 Department of Pathology, Diakonessenhuis Utrecht, The Netherlands; 4 Department of Surgery, Diakonessenhuis Utrecht Received 11 March 2008; revised 25 June 2008; accepted 1 July 2008 Background: The prognostic meaning and thus indication for adjuvant therapy of lymphogenic micrometastases in breast cancer patients is still under debate. Patients and methods: From 1999 to 2007, 703 patients with c T 1 2 N 0 breast cancer underwent surgery including sentinel lymph node biopsy. Examination of sentinel lymph nodes consisted of hematoxylin and eosin and immunohistochemistry staining following serial sectioning of the sentinel node. Patients were divided into four groups: pn 0 (n = 423), p N 1micro (n = 81), p N 1a (n = 130) and p N 1b (n = 69). Median follow-up was 40 months. Results: At the end of follow-up, 53 patients had died and 64 had recurrent disease. Compared with p N 0 and following adjustment for possible confounders, including adjuvant systemic treatment, overall survival was not significantly different for p N 1micro while significantly worse for p N 1a and p N 1b {hazard ratio (HR) [95% confidence interval (CI)]: 0.59 [ ], 4.31 [ ], [ ], respectively}. Likewise, disease-free survival was not significantly different for p N 1micro and worse for p N 1a and p N 1b (HR [95% CI]: 1.43 [ ], 2.79 [ ], 7.13 [ ], respectively). Distant metastases were more commonly observed in the p N 1micro than in the pn 0 group, but still not as common as in the p N 1a or p N 1b group (HR [95% CI]: 4.85 [ ], [ ], [ ], respectively). Conclusion: Although the risk of distant metastases was higher in patients in the p N 1micro than in the p N 0 group, no statistically significant differences were observed in overall or disease-free survival between p N 0 and p N 1micro. Micrometastatic lymph node involvement in itself should not be an indication for adjuvant chemotherapy in breast cancer patients. Key words: breast cancer, micrometastases, prognosis, sentinel lymph node introduction Axillary staging is a hallmark of breast cancer surgery as metastatic lymph node involvement is a strong prognosticator. The presence of lymphogenic metastases and number of involved lymph nodes contribute importantly to adjuvant systemic treatment decisions. In the era of the sentinel lymph node biopsy (SLNB), lymph nodes are assessed more thoroughly for tumor involvement than before. Consequently, the proportion of patients diagnosed with micrometastatic lymph node involvement (i.e. tumor deposits >0.2 and <2 mm) has increased [1 7], and micrometastases are observed in up to 23% of breast cancer patients [1, 6, 8]. These micrometastases pose a clinical dilemma with regard to adjuvant treatment decisions because their prognostic meaning is currently unclear. Most studies on this topic originate from the pre-slnb era, are retrospective and yield *Correspondence to: Dr T. van Dalen, Department of Surgery, Diakonessenhuis Utrecht, Bosboomstraat 1, 3582 KE Utrecht, The Netherlands. Tel: ; Fax: ; tvdalen@diakhuis.nl inconsistent results. Some earlier reports indicated a prognosis of patients with TNM (tumor node metastasis) stage p N 1micro disease comparable to patients without lymph node involvement ( p N 0 ) [9], while others observed a prognosis comparable to patients with TNM stage p N 1a disease [10]. In this study from the SLNB era, we evaluated the association between p N 1micro disease and clinical outcome compared with patients with p N 0, p N 1a and p N 1b disease. patients and methods From June 1999 to January 2007, 720 consecutive patients with clinically T 1 2 N 0 primary invasive breast cancer underwent surgical treatment including an SLNB procedure at the Diakonessenhuis Utrecht (a large regional teaching hospital in The Netherlands). These women were all enrolled in the current study. Data regarding demography, preoperative lymphoscintigraphy, operative procedure, pathology results and adjuvant treatment administration were collected prospectively. At the time of the introduction of the sentinel node procedure, the ethical committee of the hospital approved the routine use of the SLNB as a staging procedure. All patients received written information regarding the SLN procedure. original article ª The Author Published by Oxford University Press on behalf of the European Society for Medical Oncology. All rights reserved. For permissions, please journals.permissions@oxfordjournals.org

2 Annals of Oncology Patients who presented with a synchronous contralateral breast cancer (n = 8) or with multifocal carcinoma (n = 9) were excluded to avoid difficulty of ascribing patient outcome to tumor-specific lymph node status. The cohort available for analysis consisted of 703 patients. SLN procedure On the day of the operation, all patients received a combination of peritumoral intraparenchymal and s.c. injections of an average of 77.7 MBq ( MBq) 99m Tc nanocolloid. Continuous visualization was done and imaging started as soon as lymphatic drainage was visualized on the persistence scope and at 2 3 h after injection in both the anterior and the lateral direction. The operative procedure was done in the afternoon of the same day. A c-ray detection probe was intraoperatively used for SLN identification. During the operation, both axillary and internal mammary (IM) sentinel nodes were retrieved. Axillary SLNs were visualized on lymphoscintigraphy and collected by axillary exploration in 99% of the patients. IM SLNs were visualized in 22% of the patients, and in 78% of the patients with visualized IM SLNs they could be successfully retrieved through an intercostal exploration. Detailed information about this procedure was presented earlier by our study group [11]. pathologic examination of the SLN Intraoperative frozen section analysis of the axillary SLNs was done to enable axillary dissection during the same operative procedure in case of overt lymph node metastases. In addition, both axillary and IM SLNs were formalin fixed and paraffin embedded and four cuts from both halves were taken at 250-lm intervals starting from the center. The sections were stained with both hematoxylin and eosin (H&E) and immunohistochemically with an antibody against keratin. When the axillary SLN contained metastases, a subsequent axillary dissection was carried out, either during the first operation when the frozen section analysis revealed metastases or as a second operation when the metastases were detected on the paraffin slices. classification of lymph node stage On the basis of the pathologic findings of the SLN and the axillary dissection specimens, lymph node status was classified according to the 6th edition of the International Union Against Cancer (UICC) TNM classification [12]. pn 0 : no regional lymph node metastasis; pn itc : clusters of tumor cells in regional lymph nodes <0.2 mm; pn 1micro : metastasis in axillary lymph nodes with a size between 0.2 and 2.0 mm; pn 1a : 1 3 axillary macrometastasis (at least one with size >2.0 mm); pn 1b : a single positive IM lymph node (diagnosed by SLNB, not clinically apparent); pn 1c : a combination of p N 1a and p N 1b ; pn 2a : 4 9 ipsilateral axillary macrometastases; pn 3a : 10 axillary macrometastases. According to the UICC TNM classification, p N itc was classified as p N 0. nonoperative treatment On the basis of the axillary lymph node status and primary tumor characteristics, adjuvant systemic and/or radiotherapeutic treatment was given in accordance with the Dutch national guidelines [13]. The finding of macrometastatic disease in the axillary lymph nodes or IM lymph node metastases (TNM stage p N 1a c / p N 2 / p N 3 ) were indications for adjuvant therapy. Furthermore, primary tumor size, hormonal receptor status [estrogen receptor (ER) and progesterone receptor (PR)], modified Bloom Richardson (BR) malignancy grade (classified according to the Nottingham modification [14]) and patient age were taken into account. In patients with p N 1micro disease and favorable primary tumor characteristics, the guideline states that it is not clear whether the prognosis of TNM stage p N 1micro justifies adjuvant systemic treatment [13, 15, 16]. The uncertain benefit of, and indication for, adjuvant systemic treatment was discussed with all patients by the medical oncologist and the choice to give hormonal therapy and/or chemotherapy was made by the physician and the patient. follow-up Follow-up started at the date of first operation. Patients were routinely seen twice yearly during outpatient visits, and a mammography was made annually. Dates of subsequent locoregional recurrence, contralateral breast cancer, osseal or visceral metastasis and death were recorded prospectively until August General practitioners were actively contacted for additional information when patients had not visited the hospital for 12 months. analysis Several patients had co-variables with missing values: tumor size (n = 4), modified BR grade (n = 5), mitotic activity index (n = 14), PR status (n = 1), human epidermal growth factor receptor 2 (HER2)/neu status (n = 120), adjuvant radiotherapy (n = 3), adjuvant hormonal therapy (n = 22) and adjuvant chemotherapy (n = 22). As it has been shown that the analysis of data after omitting patients with a missing value reduces statistical power and often lead to a biased result, we used an imputation method to replace missing values [17, 18]. This was done for all variables with missing data except for HER2/neu status, which was deemed to be missing in too many patients (17%, due to the relatively recent introduction of HER2/neu assessment in clinical practice). In total, 40 patients (6%) with missing data on one or more co-variables had these values imputed by an expectation maximization method [Missing Value Analysis command, SPSS 14.0 (SPSS, Chicago, IL)]. For this, we used all co-variables including information on outcome and lymph node status. All analyses that we report are on the basis of this dataset with imputed values, but we also analyzed the data using a complete-case approach to evaluate the robustness of our findings. On the basis of the metastatic involvement of regional lymph nodes, patients were categorized into four groups for analysis: p N 0 (including pn itc ), p N 1micro, p N 1a and p N 1b. Then, p N 0, p N 1micro, p N 1a and p N 1b groups were compared for differences in age, tumor characteristics and adjuvant therapy administration by plotting their mean (with standard deviation) or median (with range) for continuous data when appropriate and percentages for categorical data within each group. Differences were tested for statistical significance by one-way analysis of variance, Kruskal Wallis test or chi-square test when applicable. We assessed the association between lymph node status, with special interest in the p N 1micro group, and patient outcome in several ways. End points were defined as overall survival (OS), disease-free survival (DFS) and its individual components (i.e. locoregional recurrence, contralateral breast cancer and osseal or visceral metastasis). First, incidence rates of these outcomes were calculated for the total study population. Then, crude and age-adjusted incidence rates for each group were calculated (for the latter using the indirect standardization method in which p N 0 group served as the standard). Cox proportional hazards analyses were used to assess the risk of adverse patient outcome for p N 1micro, p N 1a and p N 1b compared with the p N 0 group. For OS analyses, follow-up ended at the date of death (event) or either at the date of lost to follow-up or at the end of follow-up (by censoring), whichever occurred first. For DFS analyses, follow-up ended as event at the date of death, locoregional recurrence, contralateral breast cancer or metastasis, whichever occurred first (women remaining free of 42 Gobardhan et al. Volume 20 No. 1 January 2009

3 Annals of Oncology original article disease until lost to follow-up or until the end of follow-up were censored at that date). For analyses regarding risk of metastasis per se, osseal or visceral metastasis, follow-up ended as event at the first occurrence of the specific outcome (women remaining free of the specific outcome until death, lost to follow-up or end of study were censored at that date). No Cox proportional hazards analyses were carried out for the risk of locoregional recurrence and contralateral breast cancer as the number of these events was deemed too small. Several models were made for each outcome of interest: a model without adjustment for co-variables (crude model); a model with adjustment for age (continuous), tumor size (continuous) and BR grade (adjusted model 1) and a model with additional adjustment for adjuvant treatment (adjusted model 2). We explored whether continuous variables (age and tumor size) were nonlinearly related with the different outcomes by adding quadratic terms to the adjusted model 2. This did not improve the fit of the models, so transformation of these variables was not deemed necessary. Categorical variables were entered into the models by making use of dummy variables. Selection of co-variables to include in the multivariate models was on the basis of a statistical significant univariate association with lymph node status. Survival and hazard plots visualizing the relation between lymph node status and the different outcomes were derived from the Cox proportional hazards analyses (adjusted model 2, plotted in strata of lymph node status at the mean of the co-variables). The proportionality of the hazard assumption was checked by log minus log plots and was not violated for any of the variables in the different models. We also assessed the magnitude of correlations between all estimates within the different models and found that there was no threat of multicollinearity. All analyses were carried out with SPSS 14.0 (SPSS), and all tests were two-sided with a cut-off for statistical significance of 5%. results Table 1. Baseline characteristics according to lymph node status in 703 c T 1 2 breast cancer patients At the end of follow-up (1 August 2007), 636 women of the cohort of 703 women were still alive (90.5%), 53 had died (7.5%) and 14 were lost to follow-up (2.0%). A total of months of follow-up were accrued, with a median time of follow-up of 40 months. The median age of the patients was 59.4 (range ) years. There were 423 patients in the p N 0 group (60.2%), among them there were 28 patients with p N itc. Characteristic Lymph node status P pn 0 (n = 423) pn 1micro (n = 81) pn 1a (n = 130) pn 1b (n = 69) Accrued months of follow-up Age (years) a 61.6 ( ) 56.5 ( ) 56.2 ( ) 54.6 ( ) c Age (%) <35 years years years e Tumor size (cm) b 1.6 (0.8) 1.9 (0.8) 2.1 (1.0) 2.2 (0.9) <0.001 d Tumor size (%) <1 cm cm cm cm <0.001 e Bloom Richardson grade (%) Well differentiated Moderately differentiated Poorly differentiated e Mitotic activity index a 4 (0 92) 4 (0 66) 5 (0 50) 5 (0 72) 0.68 c Mitotic activity index (%) < e Estrogen receptor positive (%) e Progesterone receptor positive e (%) HER2/neu positive (%) e Records with missing values that were imputed (see patients and methods section): tumor size, 4; modified Bloom Richardson grade, 5; mitotic activity index, 14; progesterone receptor status, 1. For 120 records, human epidermal growth factor receptor 2 (HER2)/neu status was unknown, these values were not imputed. Percentages may not total 100% due to rounding. a Median (range). b Mean (standard deviation). Statistical tests: c Kruskal Wallis d One-way analysis of variance e chi-square. Volume 20 No. 1 January 2009 doi: /annonc/mdn535 43

4 Annals of Oncology There were 81 in the p N 1micro group (11.5%), 130 in the p N 1a group (18.5%) and 69 in the p N 1b group (9.8%). This latter group contained four (5.8%) patients classified as p N 1b,14 (20.3%) as p N 1c, 27 (39.1%) as p N 2a and 24 (34.8%) as p N 3a/b. Various baseline characteristics were not evenly distributed between the groups (Table 1). Higher nodal status was Table 2. Adjuvant therapy according to lymph node status in 703 c T 1 2 breast cancer patients Therapy Lymph node status P a pn 0 pn 1micro pn 1a pn 1b (n = 423) (n = 81) (n = 130) (n = 69) Radiotherapy (%) Hormonal therapy (%) <0.001 Chemotherapy (%) <0.001 Records with missing values that were imputed (see patients and methods section): adjuvant radiotherapy, 3; adjuvant hormonal therapy, 22; adjuvant chemotherapy, 22. Statistical tests: a chi-square. Table 3. Hypothetical indication for adjuvant systemic treatment in the pn 1micro group when p N 1micro was considered as p N 0 or p N 1a Therapy pn 1micro considered as p N 0 pn 1micro considered as p N 1a Actually treated Hormonal therapy (%) Chemotherapy (%) associated with younger age, larger primary tumor size and higher BR grade. The proportions of ER-positive, PR-positive and HER2/neu-positive tumors were not different for all N- categories. adjuvant postoperative treatment Adjuvant hormonal therapy and chemotherapy were given more frequently with increasing nodal status (Table 2). In the pn 1micro group, 26% underwent chemotherapy while 65% received hormonal therapy. Compared with the situation where the p N 1micro group would have been treated strictly as patients with p N 0 disease (on the basis of primary tumor and patient characteristics), the proportion of p N 1micro patients actually receiving chemotherapy was as high as expected, while hormonal therapy was given twice as often. Similarly, compared with a strict treatment regimen as applied to p N 1a disease, p N 1micro patients were less often treated with adjuvant hormonal therapy and chemotherapy (Table 3). patient outcome During the observation period, 53 patients died, and the overall annual death rate was 2.3% (Table 4). Thirty patients died with and 23 without breast cancer recurrence. Breast cancer recurred in 64 patients: distant metastasis (n = 44), locoregional relapse (n = 14) and contralateral breast cancer (n = 14). The annual rates were 0.6% for locoregional recurrence, 0.6% for contralateral cancer and 1.9% for metastases (visceral: 1.3%; bone: 1.5%). After adjustment for differences in age, tumor size and BR grade, OS in the p N 1micro group was not significantly different when compared with women with p N 0 disease [hazard ratio (HR) 0.43; 95% confidence interval (CI) ]. In Table 4. Lymph node status and (disease-free) survival for 703 c T 1 2 breast cancer patients in a crude model, after adjustment for age, tumor size and Bloom Richardson (BR) grade a and after additional adjustment for adjuvant treatment b No. of patients Follow-up c No. of events Incidence rate d Age-adjusted Crude model Adjusted model 1 a Adjusted model 2 b survival rate d Hazard ratio P Hazard ratio P Hazard ratio Disease-free survival All pn (referent) 1.00 (referent) 1.00 (referent) pn 1micro ( ) ( ) ( ) 0.36 pn 1a ( ) ( ) ( ) pn 1b ( ) < ( ) < ( ) <0.001 Overall survival All pn (referent) 1.00 (referent) 1.00 (referent) pn 1micro ( ) ( ) ( ) 0.49 pn 1a ( ) ( ) ( ) pn 1b ( ) < ( ) < ( ) <0.001 P Follow-up 40 months. CI, confidence interval. a Adjusted by Cox regression analysis for age, tumor size and BR grade. b Additionally adjusted by Cox regression analyses for radiotherapy, hormonal therapy and chemotherapy. c Follow-up time in months. d Incidence rate per 1000 women per year. 44 Gobardhan et al. Volume 20 No. 1 January 2009

5 Annals of Oncology comparison to patients with p N 0 disease, OS was significantly and gradually worse for p N 1a and p N 1b patients (HR 2.44, 95% CI , and HR 5.90, 95% CI , respectively; Table 4 and Figure 1a). The differences in OS between p N 1a and pn 1b patients compared with p N 0 patients increased when the multivariate analysis was additionally adjusted for adjuvant therapy, while results for p N 1micro patients did not change (Table 4). DFS was not significantly different in the p N 1micro or p N 1a group compared with p N 0 patients (age-, tumor size- and BR grade-adjusted HR 0.99; 95% CI , and HR 1.39; 95% CI , respectively), but was significantly worse for p N 1b patients (age-, tumor size- and BR gradeadjusted HR 3.30, 95% CI ; Table 4 and Figure 1b). Additional adjustment for adjuvant therapy did not change the results for the p N 1micro group, but again strengthened the associations for both the p N 1a and the p N 1b groups leading to a significant increased risk in the p N 1a group (Table 4). There was a proportional increased risk of distant metastases in relation to metastatic lymph node involvement (Table 5). Women with p N 1micro disease had an almost three times higher risk of any distant metastases than p N 0 patients (age-, tumor size- and BR grade-adjusted HR 2.93; 95% CI ). The risk of visceral metastasis was not significantly increased, but the risk of bone metastasis was borderline significantly increased when adjusted for age, tumor size and BR grade (HR 2.88; 95% CI ) and reached statistical significance after additional adjustment for adjuvant treatment (Table 5). Women with p N 1a disease had about a five times higher risk of both visceral and osseal metastases compared with the p N 0 group, whereas women with p N 1b disease had a 14 times increased risk of visceral and an eight times increased risk of osseal metastases, all when adjusted for age, tumor size and BR grade. Additional adjustment for adjuvant therapy strengthened these associations, retaining similarly increased risks of visceral and osseal metastases in p N 1a patients, and a predominantly higher increased risk of visceral metastases compared with osseal metastases in the p N 1b group (Table 5 and Figure 2a and b). Analyzing the data without imputation of missing values yielded largely similar results. Such a complete-case analysis tended to result in somewhat stronger relations (on average 4% inflation of effect estimates; standard deviation 8%). Conclusions on the basis of statistical significance were similar between the two approaches (data not shown). discussion In a prospective cohort of patients who underwent surgery for clinically T 1 2 N 0 breast cancer and staging by SLNB, micrometastatic lymph node involvement was observed in 11.5% of the patients. After a limited follow-up and following adjustment for age, tumor size, modified BR malignancy grade and adjuvant systemic therapy, we found OS to be comparable to patients with p N 0 disease and DFS closely resembling p N 0 disease too. The risk of distant metastases was, however, gradually higher for every subsequent N-category. original article Figure 1. (A) Overall survival for c T 1 2 breast cancer patients, median follow-up 40 months, on the basis of the Cox proportional hazards analyses adjusted for age, tumor size, BR grade and adjuvant treatment. (B) Disease-free survival for c T 1 2 breast cancer patients, median follow-up 40 months, on the basis of Cox proportional hazards analyses adjusted for age, tumor size, BR grade and adjuvant treatment. This study has several strengths. First, SLNs were uniformly examined by serial sectioning at 250-lm intervals. As a confirmation of the thoroughness of the standardized pathology examination, the SLNB procedure resulted in the observed high frequency of patients with TNM stage p N 1micro in this study group. This is in line with other SLNB-series reporting frequencies of micrometastases up to 23% [1,6 8]. Another quality-enhancing consequence of the SLNB procedure was the exploration for IM SLNs. This led to the exclusion of patients with IM metastases ( p N 1b and p N 1c ) that Volume 20 No. 1 January 2009 doi: /annonc/mdn535 45

6 Annals of Oncology Table 5. Lymph node status and risk of metastases for 703 c T 1 2 breast cancer patients in a crude model, after adjustment for age, tumor size and Bloom Richardson (BR) grade a and after additional adjustment for adjuvant treatment b No. of patients Follow-up c No. of events would otherwise have been classified as p N 1a. In addition, the present series is a substantial cohort of patients with almost no lost to follow-up. The main weakness of the present study was the limited follow-up period resulting in a small number of events. Consequently, firm conclusions are difficult to make. However, as the SLNB procedure is only used since the late 1990s, more mature data, although urgently needed [19], are not at hand. Furthermore, adjuvant systemic treatment in the p N 1micro group was a potential source of bias. Hormonal therapy was prescribed twice as often as one would have advised on the basis of the primary tumor characteristics and the age of the patient, reflecting a tendency to give hormonal therapy in patients with p N 1micro. Chemotherapy was only given to the proportion of patients in whom age and primary tumor characteristics justified its use. Recognizing the possibility of the treatment bias we therefore presented the multivariate analyses both without and with adjustment for adjuvant treatment. Lastly, although SLNB has largely improved staging of breast cancer patients, there remains a small but realistic chance of missing micrometastases when examining SLNs following serial sectioning lymph nodes at 250-lm intervals as proposed by our national pathology guidelines [20] and what appears to be common clinical practice [21]. The prognostic significance of lymphogenic micrometastatic disease is still under debate. Older studies report equivocal results. Some observed a prognosis for p N 1micro comparable to the prognosis of p N 0 patients [9, 22, 23], while others found the prognosis of p N 1micro to be similar to p N 1a patients [10,24 Incidence Age-adjusted Crude model Adjusted model 1 a Adjusted model 2 b rate d incidence rate d Hazard ratio P Hazard ratio P Hazard ratio Metastasis all All pn (referent) 1.00 (referent) 1.00 (referent) pn 1micro ( ) ( ) ( ) pn 1a ( ) ( ) ( ) <0.001 pn 1b ( ) < ( ) < ( ) <0.001 Metastasis visceral All pn (referent) 1.00 (referent) 1.00 (referent) pn 1micro ( ) ( ) ( ) 0.25 pn 1a ( ) ( ) ( ) <0.001 pn 1b ( ) < ( ) < ( ) <0.001 Metastasis osseal All pn (referent) 1.00 (referent) 1.00 (referent) pn 1micro ( ) ( ) ( ) pn 1a ( ) < ( ) ( ) <0.001 pn 1b ( ) < ( ) < ( ) <0.001 Follow-up 40 months. CI, confidence interval. a Adjusted by Cox regression analysis for age, tumor size and BR grade. b Additionally adjusted by Cox regression analyses for radiotherapy, hormonal therapy and chemotherapy. c Follow-up time in months. d Incidence rate per 1000 women per year. 26]. A number of recently conducted large population-based studies observed OS for p N 1micro patients to be between p N 0 and p N 1a, with a modestly increased risk of death for p N 1micro versus p N 0 [27 30]. The aforementioned studies invariably report on patients treated in the pre-sln era. Before the introduction of the SLNB as a staging procedure in breast cancer surgery, the routine pathological examination of lymph nodes from axillary dissection specimens was done by halving the lymph nodes and examining one cut from both halves by H&E only. Nowadays, lymph nodes are investigated by serial sectioning a node at very small intervals. In the present study, 10 slices per node were examined. In addition, not only the number of examined cuts of lymph nodes has changed but also the routine use of immunohistochemical staining with antibodies against keratin has facilitated the detection of very small clusters of metastatic tumor cells in lymph nodes. While the population-based studies from the pre-sln era reported a 2% 5% frequency of p N 1micro, we observed 11.5% of patients with TNM stage p N 1micro and others found similar or even higher rates of micrometastases since the introduction of the SLN procedure. In part, this higher frequency is the result of patient selection since overt axillary metastases preclude the use of the SLNB, and these patients are not included in SLN cohorts. On the other hand, and undoubtedly more importantly, better examination of lymph nodes has contributed to the observed higher frequency of micrometastases. Not only has the frequency of lymphogenic micrometastases increased, at the same time even smaller, P 46 Gobardhan et al. Volume 20 No. 1 January 2009

7 Annals of Oncology Figure 2. (A) Cumulative incidence of osseal metastasis in 703 c T 1 2 breast cancer patients, median follow-up 40 months, on the basis of the Cox proportional hazards analyses adjusted for age, tumor size, BR grade and adjuvant treatment. (B) Cumulative incidence of visceral metastasis in 703 c T 1 2 breast cancer patients, median follow-up 40 months, on the basis of the Cox proportional hazards analyses adjusted for age, tumor size, BR grade and adjuvant treatment. so-called sub-micrometastases are detected in a substantial proportion of the patients [3, 7, 31], and within the p N 1micro group the smaller metastases appear to prevail [31]. Apart from the stage-migrating effect of the SLN procedure, adjuvant systemic treatment has changed substantially in the same period. During the last 10 years, determination of endocrine responsiveness of primary breast cancers has original article improved largely, resulting in an increasing proportion of ERpositive patients and a similar rise of patients who will receive endocrine therapy. Furthermore, and also taking place in the last decade, more patients receive adjuvant systemic therapy because of unfavorable tumor characteristics dictated by more strict St Gallen criteria [32]. Lastly, again in the same time frame, more potent (anthracycline-containing) drugs are being used [15, 33]. The current group of p N 1micro patients that consists of patients with lesser metastatic burden being more aggressively treated is different from the group of patients who were diagnosed as having p N 1micro before the introduction of the SLN procedure. Consequently, we argue that the prognostic value of p N 1micro cannot be distilled from studies on the basis of studies of patients who were staged by axillary lymph node dissections. The most robust data from the SLN era come from a study by Colleoni et al. from the European Cancer Institute in Milan. After 4 years of follow-up, they observed disease-free, as well as metastasis-free survival for the p N 1micro group to be worse than p N 0, with a hazard rate of 1.5 for DFS. However, OS was exactly the same after 4 years of follow-up and significantly better than OS of patients with p N 1a disease [31]. It is noteworthy that the cohort of patients was not exclusively staged by the SLN procedure. Almost half of the 1959 patients in this study underwent axillary dissection as a staging procedure. Furthermore, p N 1micro was considered an indication for adjuvant systemic therapy in their study. In agreement with Colleoni, we found OS for p N 1micro patients to be comparable to p N 0 patients, and distant metastases were significantly more common in the p N 1micro group. In contrast with the Milan group, patients with p N 1micro were not routinely prescribed chemotherapy in the present study, and only 25% received adjuvant chemotherapy. One explanation for the paradoxical observation that a difference in DFS did not translate into a difference in OS may be that the follow-up period is too short. Another explanation is our finding that there was a difference in bone and visceral metastases between the p N 1micro group and the pn 1a group. Visceral metastases, associated with a gloomy short-term prognosis, were not more common in the p N 1micro group than in the p N 0 group, while osseal metastases showed a proportional increase in relation to all N-categories. Lastly, competing other causes of death may also be an explanation for the fact that a difference in metastasis-free survival does not translate into a difference in OS. Furthermore, although we observed a significantly higher risk of distant metastases in the p N 1micro group and a not significantly worse DFS, the hazard rates for these end points were at least twice as high for the p N 1a group. This implies that for all end points, the outcome in patients with p N 1micro disease is at least better than that for patients with p N 1a disease. The relevance of the prognostic meaning of p N 1micro is the answer to the clinical problem as to whether p N 1micro should be an indication for adjuvant systemic treatment. Although follow-up is very limited, and despite the fact that clinicians tend to give hormonal therapy on the basis of the finding of micrometastases, the present data do not support the use of adjuvant systemic treatment in patients only because they have Volume 20 No. 1 January 2009 doi: /annonc/mdn535 47

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