Recent Trends in U.S. Breast Cancer Incidence, Survival, and Mortality Rates

Transcription

1 Recent Trends n U.S. Breast Cancer Incdence, Survval, and Mortalty Rates Kenneth C. Chu, Robert E. Tarone, Larry G. Kessler, Lynn A. G. Res, Benjamn F. Hankey, Banj A. Mller, Brenda K. Edwards* Background: Clncal trals have demonstrated that use of mammographc screenng and advances n therapy can mprove prognoss for women wth breast cancer. Purpose: We determned the trends n breast cancer mortalty rates, as well as ncdence and survval rates by extent of dsease at dagnoss, for whte women n the Unted States and consdered whether these trends are consstent wth wdespread use of such benefcal medcal nterventons. Methods: We examned mortalty data from the Natonal Center for Health Statstcs and ncdence and survval data by extent of dsease from the Survellance, Epdemology, and End Results Program of the Natonal Cancer Insttute, all stratfed by patent age, usng statstcal-regresson technques to determne changes n the slope of trends over tme. Results: The age-adjusted breast cancer mortalty rate for U.S. whte females dropped 6.8% from 1989 through A sgnfcant decrease n the slope of the mortalty trend of approxmately 2% per year was observed n every decade of age from 40 to 79 years of age. Trends n ncdence rates were also smlar among these age groups: localzed dsease rates ncreased rapdly from 1982 through 1987 and stablzed or ncreased more slowly thereafter; regonal dsease rates decreased after 1987; and dstant dsease rates have remaned level over the past 20 years. Three-year relatve survval rates ncreased steadly and sgnfcantly for both localzed and regonal dsease from 1980 through 1989 n all ages, wth no evdence of an ncrease n slope n the late 1980s. Implcatons: The decrease n the dagnoss of regonal dsease n the late 1980s n women over the age of 40 years lkely reflects the ncreased use of mammography earler n the 1980s. The ncrease n survval rates, partcularly for regonal dsease, lkely reflects mprovements n systemc adjuvant therapy. Statstcal modelng ndcates that the recent drop n breast cancer mortalty s too rapd to be explaned only by the ncreased use of mammography; lkewse, there has been no equvalent dramatc ncrease n survval rates that would mplcate therapy alone. Thus, ndcatons are that both are nvolved n the recent rapd declne n breast cancer mortalty rates n the Unted States. [J Natl Cancer Instl996;88:1571-9] The past two decades have seen advances n the detecton, dagnoss, and treatment of breast cancer. Mammography was shown to be benefcal n reducng breast cancer mortalty n randomzed clncal trals n the early 1980s (7,2). Recommendatons to use screenng mammography begnnng at age 40 years resulted n dramatc ncreases n the number and usage of screenng mammography machnes (3-6). Subsequent clncal tral results have further demonstrated the benefts of mammography (7,5). The benefts of adjuvant therapy for both premenopausal and postmenopausal women were demonstrated n randomzed clncal trals n the late 1970s and early 1980s (9,10), resultng n recommendatons to the oncology communty regardng the use of adjuvant therapy (11,12). Results (13) have affrmed the benefts of adjuvant therapy. If the benefts demonstrated n clncal trals extend to communty medcal practce, then ncreased use of mammography should affect both the magntude of breast cancer ncdence rates and the dstrbuton of cases by extent of dsease at dagnoss, and mproved treatment regmens should result n ncreases n breast cancer survval rates, partcularly for regonal dsease. Furthermore, f these medcal nterventons are both benefcal and wdely employed, then they should eventually result n declnng breast cancer mortalty rates. Marked drops n breast cancer mortalty rates snce 1990 have been reported n the Unted States (14), England and Wales (15,16), and Canada (17), and these abrupt declnes may provde evdence of mproved medcal nterventons. Evaluaton of trends n breast cancer mortalty rates, however, s not straghtforward. Because of exstng brth cohort trends n breast cancer mortalty for whte females (18,19), care must be taken n evaluatng trends n breast cancer mortalty for evdence of a beneft due to screenng or treatment. Snce mortalty decreases are expected n certan age groups because of exstng brth cohort patterns, unantcpated or accelerated mortalty decreases are requred for evdence of screenng and/or treatment benefts (79). Examnaton of trends n breast cancer mortalty usng ageadjusted rates for all ages, or even for broad age groups, such as ages less than 65 years and ages 65 or greater, also makes nterpretaton dffcult (79). Accordngly, relatvely narrow age groupngs must be used n evaluatng breast cancer trends. In the current nvestgaton, breast cancer ncdence rates and survval rates, both by extent of dsease and age at dagnoss, and breast cancer mortalty rates by decade of age at death are examned for whte females n the Unted States. The ncdence, *Afflatons of authors: K. C. Chu (Specal Populaton Studes Branch), L. G. Kessler (Appled Research Branch), L. A. G. Res, B. F. Hankey, B. A. Mller (Cancer Statstcs Branch), B. K. Edwards (Cancer Control Research Program), Dvson of Cancer Preventon and Control; R. E. Tarone, Bostatstcs Branch, Dvson of Epdemology and Genetcs, Natonal Cancer Insttute, Bethesda, MD. Correspondence to: Kenneth C. Chu, Ph.D., Natonal Insttutes of Health, EPN 240, Bethesda, MD See "Notes" secton followng "References." Journal of the Natonal Cancer Insttute, Vol. 88, No. 21, November 6, 1996 ARTICLES 1571

2 survval, and mortalty trends are analyzed for sgnfcant changes, and the extent to whch such changes are consstent wth early detecton and successful treatment of breast cancer s dscussed. Materals and Methods Incdence and survval rates were obtaned from populaton-based data collected by the Survellance, Epdemology, and End Results (SEER) Program 1 of the Natonal Cancer Insttute (2021). These rates are based on all whte female breast cancer cases dagnosed from 1973 through 1993 (22) among resdents of nne geographc areas: Connectcut, Hawa, Iowa, New Mexco, Utah, Atlanta, Detrot, Seattle-Puget Sound, and San Francsco-Oakland. Annual ncdence rates are age standardzed to the 1970 U.S. populaton by drect standardzaton (25). On the bass of past SEER experence, the ncdence rates currently reported for the most recent year (.e., 1993) are 3%-4% lower than the actual ncdence rates because of ncomplete ascertanment (24). Investgatons nto survval are based on 3-year relatve survval rates (2526) by tumor extent at dagnoss. Categores of tumor extent at dagnoss used n ths report are n stu, localzed, regonal, and dstant dsease. The total nvasve ncdence rates nclude all staged cancers as well as unstaged cancers, but exclude n stu cases. In stu lesons have not penetrated the basement membrane. Localzed dsease refers to nvasve neoplasms confned entrely to the breast. Regonal dsease refers to a neoplasm that extends beyond the lmts of the breast drectly nto surroundng tssues/organs or nvolves regonal lymph nodes. Dstant dsease refers to a neoplasm that has metastaszed to remote stes of the body. Unstaged dsease denotes cases for whch nsuffcent nformaton was avalable to permt the accurate assgnment of a stage (24). Breast cancer mortalty data from 1969 through 1993 were from the Natonal Center for Health Statstcs (NCHS). The NCHS receves death certfcates for all 50 states and comples mortalty rates by race, sex, age, year of death, and cause of death. The current study ncludes all deaths of whte females n the Unted States, wth breast cancer lsted as the underlyng cause of death (27). Mortalty rates are age adjusted by drect standardzaton to the 1970 U.S. populaton. Breast cancer mortalty rates for whte females n the SEER areas follow the same general trend seen n total U.S. rates but wth consderably greater varablty. Lnear regresson analyses of log-transformed rates were used to quantfy the drecton and magntude of trends n breast cancer survval and mortalty rates; all reported P values arc two-taled. Pecewse regresson analyses were used to test for a sudden change n the slope of the lnear trend n rates (Appendx). For mortalty rates, the trend for all ages was analyzed frst, and then the trends by decade of age were examned to determne the consstency of the change n the slope dentfed for all ages. Wth the excepton of the and year age groups, all regresson analyses started wth the year Mortalty curves for women years of age and years of age were not lnear from 1980 through 1990 due to downturns begnnng n the md-1980s. As a result, pecewse regresson analyses for the and year age groups begnnng n 1980 would gve exaggerated estmates of the magntude of the downturn n the 1990s. Accordngly, the pecewse regresson analyses for these age groups started n 1984 for the year group and 1985 for the year group, so that recent changes n mortalty rates could be evaluated relatve to prevously exstng decreasng trends. For the survval rates, trends n 3-year relatve survval rates from 1975 through 1989 were evaluated for all cases, for localzed dsease, for regonal dsease, and for dstant dsease; to obtan stable rates for each extent of dsease classfcaton by age, trends were evaluated n three broad age groups (.e., <50 years of age, years of age, and 270 years of age at dagnoss). Results The age-adjusted breast cancer mortalty rates for whte females of all ages from 1969 through 1993 are shown n Fg. 1. Whle breast cancer mortalty ncreased slghtly n the 1980s, there was a sharp decrease n breast cancer mortalty after Pecewse regresson ndcates a sgnfcant (P<\0~*) decrease n Af / \ & Fg. 1. Age-adjusted breast cancer mortalty rates for U.S. whte females of all ages, standardzed to the 1970 U.S. populaton I 1S Year of Death ARTICLES Journal of the Natonal Cancer Insttute. Vol. 88. No. 21, November

3 the slope of the mortalty curve for all ages (Table 1), wth the change n slope after Breast cancer mortalty curves by decade of age are shown n Fg. 2. The results of the pecewse regresson analyses for each age group assumng a change n slope after 1989 are summarzed n Table 1. The slope decreased sgnfcantly by about 2% per year after 1989 n the , , , and year age groups. The year age group had a nonsgnfcant decrease of 2.9% per year n the slope, but ths was due prmarly to a sharp 1-year declne n The age-adjusted breast cancer ncdence rates for all ages by extent of dsease at dagnoss are shown n Fg. 3, A. The stagespecfc ncdence rates for age groups 40-49, 50-59, 60-69, 70-79, and 80 years or older all had patterns very smlar to that observed for all ages. Incdence rates by stage at dagnoss are shown n Fg. 3, B, for the year age group. As wth the rates for all ages, total nvasve breast cancer ncdence rates stablzed after All age groups aged 40 years or more also showed the marked ncrease n localzed and n stu dsease rates followng The ncrease n localzed dsease abated only slghtly followng 1987 n the year and 80 years or more age groups, but subsded consderably, showng only slght ncreases followng 1987 n the , , and year age groups. All age groups over age 40 years also showed decreasng regonal dsease rates after 1987, wth stable dstant dsease rates over the entre perod from 1973 through The stage-specfc ncdence rates for nvasve dsease n the year age group dffered from those n older women (Fg. 3, C); nvasve cancer rates were level or slghtly declnng for each stage durng the 1980s. Breast cancer 3-year relatve survval rates for all nvasve cancer and for localzed and regonal dsease by age groups from 1975 through 1989 are shown n Fg. 4. Pecewse regresson ndcated a sgnfcant mprovement n survval around 1980, partcularly n women under the age of 70 years. Thus, analyses were restrcted to survval rates after The slopes of the survval curves for all nvasve dsease, localzed dsease, regonal dsease, and dstant dsease by age group are gven n Table 2. Survval rates ncreased sgnfcantly n all age groups Table 1. Annual percentage change n breast cancer mortalty rates from 1980 through 1993 estmated by pecewse regresson analyss wth a change n slope from 1989 through 1993 Age,y All ages 30-39* * :80 Slope of trend from 1980 through 1989* 0.4 ±0.1 (/>=.0005) -2.3±0.8(/>=.018) -0.0±0.2(/>=.90) -0.7 ±0.1 (/> =.0003) -O.3±0.3(/ > =.39).4 ± o. (^ICT 4 ) 1.3 ±0.1 (P<O~^) Change n slope after 1989*,t -2.2±0.2(/ 3 <10" 4 ) -2.9 ± 1.5 {P =.U) -2.4 ± 0.7 (P =.007) -2.0 ± 0.4 (P =.0007) -1.7 ± 0.5 (Z^.013) -2.2±0.3(/ > <l(t 4 ) -0.5 ± 0.4 (P =.20) * Values = least-squares estmate of slope ± standard error. tmeasures the amount the slope changed after 1989; the slope of the mortalty curve followng 1989 s the sum of the slope from 1980 through 1989 and ths change n slope. Regresson analyss begns n 1984 for the year age group and n 1985 for the year age group because ther mortalty curves are not lnear over the entre perod from 1980 through for localzed and regonal dsease. The slopes ncreased wth age for both localzed and regonal dsease, and there was no sgnfcant change n survval trends n the 1980s. Dscusson The decrease n breast cancer mortalty from 1989 through 1993 represents a hghly sgnfcant departure from the slght ncrease n breast cancer mortalty n the 1980s (Table 1). The 6.1% drop from 1990 through 1993 and the 6.8% drop from 1989 through 1993 are the largest short-term decreases n the age-standardzed (to the 1970 U.S. populaton) breast cancer mortalty rate for all ages snce The prevous largest declne over a 3-year perod was 3.7% from 1955 through 1958, whle the prevous largest declne over a 4-year perod was 4.1% from 1955 through Breast cancer mortalty rates are declnng n every decade of age under 80 years of age, and the age-adjusted breast cancer mortalty rate s lower n 1993 than t has been at any tme snce The fnal provsonal breast cancer mortalty rates (based on 10% samples of death certfcates, and age adjusted to the 1940 U.S. populaton) for men and women combned were 11.9 and 11.5 per n 1993 and 1994, respectvely (28). Thus, there s no ndcaton that the recent marked decrease n breast cancer mortalty wll abate. A 2% per year declne n the slope of the breast cancer mortalty curve after 1989 s seen n every age group from 40 to 79 years (Fg. 2, Table 1). In the year age group, the decrease n slope was of suffcent magntude to cause a decrease n rates after 1989, despte antcpated steady ncreases resultng from an ncreasng brth cohort trend n rsk (19). The recent decrease n women years of age s largely due to decreasng brth cohort rsks for women bom after 1946 (Tarone RE, Chu KC, Gaudette LA: submtted for publcaton). When changes n mortalty occur smultaneously across several age groups, the most lkely explanaton s ether a change n codng or ascertanment or the ntroducton of mprovements n medcal nterventons. There have been no recent codng changes affectng breast cancer, and examnaton of recent mortalty trends for causes of death other than breast cancer ndcate no systematc problems wth ascertanment after Thus, medcal nterventons, such as early detecton and successful treatment, are the most probable sources for the declnes n breast cancer mortalty. Evdence for a role for mammography n the recent mortalty declnes comes from the ncreased ncdence of localzed dsease and subsequent declnng ncdence of regonal dsease n each age group over 40 years. These changes suggest that mammography has led to stage shfts from regonal to localzed dsease as cancers are detected through screenng before they can progress to hgher stages (29-31). Declnng regonal dsease should eventually result n lower mortalty, because about 50% of breast cancer deaths occur n women dagnosed wth regonal dsease (32). Women under the age of 40 years show lttle change n localzed dsease ncdence rates n the 1980s, consstent wth the mnmal amount of breast cancer screenng n ths age group (3,4). The ncrease n n stu breast cancer rates n the md-1980s n women years of age ndcates some ncrease n the use of mammography n younger women, perhaps due to Journal of the Natonal Cancer Insttute, Vol. 88, No. 21, November 6, 1996 ARTICLES 1573

4 * > * < * ^ f > ( S O o S- o » < "CO QC 70 < T3 CO o CO 60 d) < V Year of Death Fg. 2. Age-adjusted breast cancer mortalty rates per for U.S. whte females by decade of age, standardzed to the 1970 U.S. populaton ARTICLES Journal of the Natonal Cancer Insttute, Vol. 88, No. 21, November 6, 1996

5 B I 8" S *&\\ I I I I I I gn 1979 gn gn IBSS 1987 I9to Year of Dagnoss S1 19fl3 10C * Yew of Dagnoss 60 s 20 Fg. 3. Age-adjusted breast cancer ncdence rates by extent of dsease at dagnoss for whte females, standardzed to the 1970 U.S. populaton: A) all ages, B) years of age, and C) years of age SS3 18*7 1«g «Yetrof Dagnoss Journal of the Natonal Cancer Insttute, Vol. 88, No. 21, November 6, 1996 ARTICLES 1575

6 - Localzed - All Cases Regonal B Year of Dagnoss - Localzed All Cases Regonal Fg. 4. Breast cancer 3-year relatve survval rates by stage at dagnoss from 1975 through 1989 for A) women less than 50 years of age at dagnoss, B) women ages years, and C) women ages 70 years or more Year of Dagnoss Localzed - All Cases - Regonal Year of Dagnoss base-lne mammograms. The decrease n nvasve breast cancer ncdence rates n women years of age n the 1980s, despte ncreasng use of dagnostc technology, reflects a marked decrease n brth cohort rsk n women bom durng the baby boom (Tarone RE, Chu KC, Gaudette LA: submtted for publcaton). The large ncreases n breast cancer ncdence rates n the 1980s have been ted to the dramatc ncrease n mammography use (33-38). Few natonal mammography utlzaton data of hgh qualty are avalable pror to 1987, but t appears that breast cancer screenng had reached perhaps 10%-20% of women over the age of 40 years by the early 1980s (59). Natonal data on the use of mammography, obtaned from three supplements to the Natonal Health Intervew Survey (NHIS) for the years 1987, 1990, and 1992, are shown n Table 3 (6). The percentages n Table 3 are for mammograms obtaned for any reason; however, data collected regardng the most recent mammogram ndcate that more than 70% of such mammograms were reported to be screenng mammograms n each age group. Usage of mammography was greatest among women ages years, wth those years old havng about the same levels of mammography as those 80 years or older. Usng the NHIS data for 1987 and 1992, a projecton model called CAN_TROL (40) was used to examne the effect of recent screenng trends on the overall age-adjusted breast cancer mortalty rates. Detals of the model have been reported (41). CAN_TROL projects cancer mortalty rates on the bass of trends n cancer preventon, screenng, and treatment actvtes. Usng NHIS screenng data, the model predcted that the ncrease n mammography use would lead to decreasng mortalty startng n the late 1980s, but the predcted declnes are not as abrupt as those actually observed followng Thus, factors 1576 ARTICLES Journal of the Natonal Cancer Insttute, Vol. 88, No. 21, November 6, 1996

7 All cases Localzed Regonal Dstant Table 2. Annual percentage changes n 3-year relatve survval rates from 1980 through 1989 Values = t^.005. tp<.05. <50* 0.49 ± 0.1 Ot 0.39 ± 0.05f 0.55 ±0.18* 1.88 ± 1.80 Womens' age, y 50-69* 0.93 ± 0.05f 0.43 ± ±0.10t 2.05 ± 0.66* least-squares estmate of slope ± standard error. 270* 1.11 ±0.19t 0.89 ± ±0.20t ± 1.09 other than mammography must be contrbutng to the observed mortalty declnes. Sgnfcant ncreases n the survval rates were observed for localzed and regonal dsease n the 1980s. The ncreases n localzed dsease survval rates may be nfluenced by the ablty of mammography to detect smaller, better prognoss, localzed lesons (36) as well as the ncreased use of breast-conservng surgery, such as lumpectomy (42). The ncrease n localzed dsease survval largely offsets the ncrease n localzed dsease ncdence rates n the 1980s, so that the contrbuton of localzed dsease to mortalty remaned relatvely constant durng the mdand late- 1980s (32,43). The ncrease n regonal-dsease survval rates would suggest a gradual mprovement n the treatment of regonal dsease. Regonal-dsease cases were prme canddates for the ntal use of adjuvant therapy, chemotherapy for premenopausal women, or tamoxfen therapy for postmenopausal women. The frst randomzed clncal trals of chemotherapy as adjuvant therapy were begun n , and the ntal fndng of beneft was reported n 1976 (9). The frst randomzed trals for tamoxfen as adjuvant therapy were begun n 1977, wth postve fndngs reported n 1983 (10). A 1985 Natonal Insttutes of Health consensus conference recommended the use of tamoxfen for postmenopausal, node-postve women wth postve estrogen receptor status and the use of chemotherapy for premenopausal, node-postve women (77). An nternatonal meetng on adjuvant therapes n early 1988 reported survval benefts for node-negatve patents (44), and n md-1988, the Natonal Cancer Insttute released a Clncal Alert to physcans recommendng adjuvant therapy for node-negatve patents (72). The gradual mprovement n survval rates s consstent wth the progressvely wder use of adjuvant therapy n the 1980s. Although no abrupt ncreases n 3-year survval rates were observed for cases dagnosed through 1989, evaluaton of longer-term survval rates, or short-term survval rates for cases dagnosed after 1989, may eventually show a survval pattern more consstent wth the observed sharp decrease n breast cancer mortalty rates after Marked declnes n breast cancer mortalty rates after 1989 have also been observed n England and Wales (15,16) and n Canada (77). To compare the decreases n dfferent countres, we computed age-adjusted breast cancer mortalty rates restrcted to women years of age, all standardzed to the U.S populaton. These age-adjusted breast cancer mortalty rates fell 9.3% n England and Wales, 9.8% n Canada, and 9.0% n the Unted States between 1989 and In England and Wales and n Canada, mass screenng wth mammography dd not begn untl the late 1980s (16,45). Breast cancer ncdence data ndcate that ncdence rates n England and Wales dd not rse sharply untl mass screenng began, but t appears that the rate of ncrease n age-specfc ncdence rates had ncreased a few years pror to the ntroducton of mass screenng (76). In Canada, ncdence rates show ncreases begnnng n the early 1980s, smlar n tmng, but somewhat smaller than those observed n the Unted States (45). It appears that mammography, although not formally offered n a mass screenng program n these countres untl the late 1980s, may have had an earler mpact on ncdence rates, perhaps through ncreased dagnostc use n the md-1980s. Thus, although mass screenng s not a plausble explanaton for the marked mortalty decreases n England and Wales or n Canada, earler dagnoss may be contrbutng to the recent mortalty decreases, as has been suggested regardng England and Wales (75). There can be lttle doubt that mproved treatment s contrbutng to the recent breast cancer mortalty decreases, and ncreased use of tamoxfen may be playng an mportant role n England and Wales (16). Nearly all patents wth breast cancer n southeast England over the age of 50 years were beng treated wth tamoxfen by as early as 1990 (76). It appears that the use of tamoxfen n U.S. patents wth breast cancer over the age of 50 years was less than that n England. In 1991 n SEER areas, adjuvant tamoxfen treatment was gven to 55% of the women over the age of 50 years who had an ntal dagnoss of early stage breast cancer and were not nvolved n a clncal tral (Harlan L: personal communcaton). For patents wth postve Table 3. Percentage of U.S. women reportng n 1987, 1990, and 1992 havng a mammogram n the past year and ever havng a mammogram* Age.y Past year Ever Past year Ever Past year Ever >80 N/At N/At Source of data: Natonal Health Intervew Survey, any mammogram. +N/A = not avalable. Journal of the Natonal Cancer Insttute, Vol. 88, No. 21, November 6, 1996 ARTICLES 1577

8 nodal status and postve estrogen receptor status, the percentage of women over 50 years treated wth tamoxfen ncreased to about 75% (Harlan L: personal communcaton). Thus, although the use of mammography was earler and greater n the Unted States, the use of adjuvant tamoxfen therapy was earler and greater n England. Despte such dfferences, the recent declne n mortalty rates n the two countres s remarkably smlar. In concluson, recent trends n breast cancer ncdence, survval, and mortalty rates for women over the age of 40 years provde evdence that both earler detecton and better treatment of breast cancer are contrbutng to the recent marked declnes n breast cancer mortalty n the Unted States. Better nformaton on the dfferences among countres n the tme of ntroducton and the extent of use of mammography and of dfferent adjuvant therapy regmens may allow a determnaton of the relatve contrbutons of earler detecton and better treatment to the recent declnes n breast cancer mortalty. Appendx Let calendar year be ndexed by ;' = 1,2,... / and the rate for the calendar year / be denoted R,. Pecewse regresson analyses (46) were performed after takng a logarthmc transformaton of rates. For each /Q from 3 to / - 2, the lnear model, a + pv + IV, (<-'ox was ft to log(/?,) usng standard multple regresson methods, where x, s defned as an ndcator functon takng the value 0 f < 0 and 1 f > 0. Thus, P2 represents the change n slope after year /r> Let /* denote the value of 0 that maxmzes the R 2 value for breast cancer mortalty data for all ages (.e., Fg. 2). If the regresson coeffcent P2* correspondng to / was sgnfcantly dfferent from 0 based on the usual / test for multple regresson parameters, then the trend n breast cancer mortalty was consdered to have a change n slope over the perod from / to / compared wth the perod 1 to /. Snce a test for changng slope was performed at 10 dfferent years (.e., 1982 through 1991), a Bonferron-adjusted sgnfcance level of 0.05/10 = was employed n the pecewse regresson analyss of mortalty rates for all ages. Regresson analyses usng untransformed and logtransformed rates gave very smlar results. (The / statstcs for testng for a change n slope vared by <2% n every year tested.) Pecewse regresson analyss wth ; = /* was appled to mortalty data for each age group to determne the consstency of the change n trend over age groups. References (/) Shapro S, Venet W, Strax P, Vend L. Ten- to fourtcen-ycar effect of screenng on breast cancer mortalty. J Natl Cancer Inst 1982:69: (2) Tabar L. Fagerberg CJ, Gad A, BaldeJorp L, Holmberg LH. Grontoft O, et al. Reducton n mortalty from breast cancer after mass screenng wth mammography. Randomsed tral from the Breast Cancer Screenng Workng Group of the Swedsh Natonal Board of Health and Welfare. Lancet 1985:1: (3) Amercan Cancer Socety. 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