chpter 3. Squmous intrepithelil lesions: cytology histology correltion CHAPTER 1 This chpter discusses the nturl history of cervicl precncer, HPV nd oncogenesis, cytology nomenclture, nd the cytologicl nd histologicl recognition of cervicl precncer. 3.1 Current understnding of the nturl history of cervicl precncer Cervicl cncer hs long precursor stge. The cervix is ccessile nd sheds exfolited cells esily, nd cytologicl exmintion of these cells revels precncerous chnges tht re esily erdicted. The essentil custive gent of cervicl cncer is the presence of high-risk HPV, which is esily detectle. Cervicl cncer is completely preventle disese. This is quite prt from the vilility of n effective vccintion. The disese should not exist. 3.2 Historicl context The precursor phse of the nturl history of cervicl cncer is chrcterized y cellulr chnges within the epithelil lining of the cervix; in other words, the normlity is entirely intrepithelil. John Willims first descried intrepithelil cellulr chnges in tissue djcent to invsive cncer more thn 125 yers go (Willims, 1888). During the erly decdes of the 20th century, the concept of intrepithelil dysplsi gined cceptnce (Cullen, 1900; Ruin, 1910). It implied cncerous-looking cells confined to the epithelium ove the sement memrne nd led to the term crcinom in situ (Broders, 1932), which ws defined s full-thickness cellulr chnges tht looked morphologiclly similr to undifferentited invsive crcinomtous cells ut were confined to the epithelium. The term dysplsi ws coined out 20 yers lter y Regn nd Hicks (1953), nd dysplsi ws ctegorized s eing mild, moderte, or severe depending on the proportion of the epithelil lyers involved in the dysplstic process. Crcinom in situ ws considered to hve greter degree of normlity nd to e the finl precncerous stte. The term koilocyte (hlo or vcuolted cytoplsm or empty spce cytoplsm) ws coined y Koss nd Durfee (1956). Meisels nd Fortin (1976) first recognized these cells s eing infected with HPV. Richrt (1968) introduced the concept of continuum nd sudivided the spectrum of normlity into three ctegories, clled CIN grdes 1 (mild dysplsi), 2 (moderte dysplsi), nd 3 (severe dysplsi). In this clssifiction, crcinom Chpter 3. Squmous intrepithelil lesions: cytology histology correltion 23
in situ ws comined with severe dysplsi. The cytologicl clssifiction ws similr in tht mild, moderte, nd severe dyskryosis were suggestive (ut not dignostic) of CIN1, 2, nd 3, respectively. The reltive ese of tretment fforded y outptient therpy, which hd egun to replce hysterectomy nd cold-knife coniztion in the 1970s nd 1980s, lowered the threshold for tretment of cervicl lesions. In n ttempt to simplify the clssifiction nd ecuse it hd ecome cler tht minor-grde lesions did not often progress to cncer, Richrt (1990) proposed two-tier clssifiction system. High-grde lesions were thought to e much more likely to e genuinely precncerous. Lowgrde lesions were considered to e trnsient nd rrely precncerous. Mny low-grde lesions were ssocited with koilocytosis nd recognized s eing HPV-relted. However, this clssifiction system ws not universlly used. Also, moderte normlities, some of which were undoutedly low-grde in nture, were included in the high-grde ctegory nd perhps treted too redily. The different clssifictions re represented in the digrm in Fig. 3.1, with tretment ptterns included elow. The trditionl screen, dignose, nd tret pthwy (Fig. 3.2) worked resonly well when the threshold for referrl to colposcopy ws set high. The concept of continuum persisted until reltively recently. A greter understnding of the iology of oncogenic HPV nd its different effects in squmous epithelium of the lower genitl trct hs led to different concept. It now seems cler tht there re two different types of HPV infection. The first type is n innocent nd trnsient infection, which my produce mild or low-grde lesions tht re recognizle cytologiclly, colposcopiclly, or histologiclly. Fig. 3.1. Chnging terminology nd tretment trends for cervicl precncer over the pst century. CKC, cold-knife coniztion; Cryo, cryotherpy; LEEP, loop electrosurgicl excision procedure; Rx, tretment. These lesions hve limited, if ny, precncerous potentil for progression to cncer. This type of infection is clled productive infection. The key step in the pthogenesis of HPVlinked cncers is the ctivtion of the virl oncogenes E6 nd E7 in the sl nd prsl cells of the infected epithelium (Bergeron et l., 2015; Doorr et l., 2012; Duensing nd Münger, 2004). If these virl genes re expressed in sl or prsl cells, they trigger chromosoml instility nd mjor numericl nd structurl ltertions of the host cell chromosomes. This leds to uneven distriution of the overll DNA content (neuploidy) nd is reflected y shifts of the nucler stining pttern (the stining intensity). This type of infection is more redily recognized cytologiclly, colposcopiclly, nd histologiclly nd is clled trnsforming infection (see Chpter 4). Sometimes moderte dyskryosis (t cytology) or moderte Fig. 3.2. Trditionl process of screening test, colposcopic ssessment, histologicl dignosis, nd tretment. 24
dysplsi (t histology) my contin oth types of infection, nd these re difficult to distinguish using cytology or histology. Fortuntely, developments in moleculr iology hve led to specific iomrkers of cell iology tht cn discriminte etween these types where dout exists (see Chpter 4). Fig. 3.3. Different HPV infection stges. 3.3 HPV nd the genesis of cervicl cncer Severl different risk fctors hve een implicted for cervicl cncer nd precncer. These include smoking, erly ge t first intercourse, nutritionl deficiency, chlmydil infection, multiple sexul prtners, multiple pregnncies, nd long-term use of orl contrceptives (Bosch et l., 1995; Frnco et l., 1999; IARC, 2007, Schiffmn et l., 1996; Wloomers et l., 1999). However, the fundmentl nd essentil custive gent is the persistence of oncogenic HPV in the epithelium of the TZ nd/or djcent glndulr epithelium. The reltionship etween oncogenic HPV nd cervicl precncer ppers, t first, prdoxicl. Cervicl cncer is lwys ssocited with oncogenic HPV, ut oncogenic HPV is norml nd usully trnsient infection tht most helthy sexully ctive women will encounter in erly reproductive life. The current thinking is tht the oncogenic HPV gins entry to the cervicl epithelium t the new SCJ, possily ssocited with minor rsions, nd tht this llows the virus to ccess reserve cells underneth the single lyer of columnr epithelium (Fig. 3.3). Most women will e infected with oncogenic HPV, nd the gret mjority will cler the infection without ny residul hrm or incresed risk of cervicl cncer. In smll percentge of women, the infection persists, nd in smll proportion of those, it ecomes integrted into the epithelil cell nuclei nd chnges from ltent to trnsforming infection. It is in those cses tht the risk of progression is high. It is not known wht distinguishes those cses in which the virus ecomes integrted nd trnsforming from those in which the infection is trnsient nd hrmless. The reltionship etween oncogenic HPV infection nd the risk of progression or clernce is discussed in Chpter 4. The crucil step is tht of the HPV infection ecoming trnsforming infection. 3.4 Cytology nomenclture To this dy, there re severl different cytologicl clssifictions for cervicl precncer. The Germn clssifiction is used in Germny, Austri, nd some countries in estern Europe. The United Kingdom hs its own clssifiction, s do Austrli nd New Zelnd. Perhps the most widely used clssifiction is the Bethesd terminology system, first introduced in 1988 y the United Sttes Ntionl Cncer Institute (Solomon, 1989). It emrced the concept of two-tier grdtion nd hs undergone severl revisions over the pst 25 yers. These revisions reflect the chnging understnding of risk ssocited with different cytologicl nd histologicl reporting nd greter understnding of the role of oncogenic HPV. The United Kingdom clssifiction now reflects the Bethesd two-tier clssifiction. To help clinicins mnge their ptients with different grdes of normlity, the ASCCP developed series of clinicl guidelines linked to the Bethesd clssifiction (Wright et l., 2003). In the United Kingdom, the NHS Cervicl Screening Progrmme (NHS, 2010) produced n evidence-sed guidelines document, which linked mngement to the degree of cytologicl normlity nd other relevnt cse chrcteristics (e.g. HPV test result, ge, nd smoking history). It hs recently een updted (NHS, 2016). Fig. 3.1 ttempts to relte some of the previous cytology nomencltures to the current Bethesd clssifiction, which is proly the most widely used system tody. There hs lwys een n interdisciplinry dependency in mngement of cervicl precncer. Trditionlly, this hs een using Chpter 3. Squmous intrepithelil lesions: cytology histology correltion 25
cytology to screen, using colposcopy to ssess nd direct iopsy, nd using histology to confirm the dignosis (Fig. 3.2). In this idelized scenrio, the cytology screening test identified cses tht my or my not hve genuine precncer, colposcopy ws le to recognize or rule out the lesion, nd colposcopiclly directed iopsy fcilitted definitive histologicl proof of disese efore tretment ws dvised. But ll three of these disciplines re sujective in nture. Until recently, histology ws considered the gold stndrd nd HSIL ws considered the threshold t which tretment ws necessry. It is now cler tht morphologicl ssessment t histology is lso less thn perfect, in prticulr the determintion of disese severity when morphologicl or histopthologicl exmintion reports HSIL-CIN2. A pper from the Lower Anogenitl Squmous Terminology (LAST) Project (Drrgh et l., 2012) finlly confirmed the reltive sujectivity of histopthology, especilly in the middle grde of CIN2. The WHO 2014 histology terminology (Kurmn et l., 2014) proposed two-tier clssifiction, HSIL nd LSIL, with the help of iomrkers to differentite the difficult or equivocl cses. occsionlly seen in the sl lyers (Fig. 3.4). Histologicl exmintion of tissue iopsy of norml squmous epithelium will revel normlly strtified epithelium with regulr mturtion nd few mitotic figures in the sl lyers. As with cytology, there will e norml nucler cytoplsmic rtios nd the nuclei will e morphologiclly norml (Fig. 3.4 nd Fig. 2.2). 3.5.2 LSIL (HPV infection; CIN1; mild dyskryosis) 3.5.2.1 Cytology The cytologicl recognition of normlity is sed on the finding of nucler enlrgement nd vrition in the size nd shpe of norml cells. An incresed intensity of stining with irregulr chromtin ptterns is nother common feture of normlity. These normlities in the superficil nd intermedite cells re koilocytosis, typicl of productive infection (LSIL). Anorml nuclei nd other cell chnges in prsl nd sl cells re typicl of trnsforming infection (HSIL). In the cse of n LSIL, s in Fig. 3.5, there is productive virl infection, nd cytology will revel enlrged nuclei with vcuolted cytoplsm in superficil nd intermedite cells. 3.5.2.2 Histology Histologicl determintion of normlity is essentilly recognition of norml cellulr prolifertion. It is sed on the morphologicl ssessment of cells in the epithelium, the rchitecture of the cellulr lyers, nd the degree of mturtion nd cellulr differentition. The reltive proportion of the epithelium tht is involved with normlity, the degree of mturtion, nd the persistence of mitotic figures throughout the epithelium re the usul prmeters used to grde the normlity. Histologicl exmintion of LSIL will revel Fig. 3.4. () Norml cytology preprtion; intermedite cells re indicted with rrows. () Norml histologicl section of squmous epithelium. 3.5 Cytologicl nd histologicl recognition of cervicl precncer 3.5.1 Norml cervicl epithelium Cytologicl exmintion of exfolited cells from the norml ectocervicl squmous epithelium will revel mostly superficil cells; the nuclei re smll, re not hyperchromtic, nd hve norml density nd shpe with norml chromtin ptterns. Crucilly, the nucler cytoplsmic rtio is low, nd mitotic figures re only Fig. 3.5. () Cytology slide of LSIL. () Histologicl section of LSIL. Koilocytosis 26
koilocytosis in the superficil lyers nd even prt of the intermedite lyer, ut the undifferentited cells will e limited to the lower third of the epithelium (Fig. 3.5). 3.5.3 HSIL (CIN2, CIN3; moderte dyskryosis, severe dyskryosis) 3.5.3.1 Cytology With severely norml CIN3 lesion, cytology will report the dignosis of HSIL. Cytology, y itself, cnnot distinguish etween CIN2 nd CIN3. The chnges seen t cytology will usully include definite increse in the nucler cytoplsmic rtio s well s norml nucler size nd density nd ltered chromtin ptterns of sl or prsl cells (Fig. 3.6). 3.5.3.2 Histology At histologicl exmintion of cler cse of CIN3, the gret mjority of pthologists will gree, ecuse the morphologicl cellulr nd Fig. 3.6. () Cytology slide of HSIL. The rrows indicte norml squmous sl cells. () Histologicl section of HSIL-CIN3. Cellulr normlity previls throughout the full thickness of the epithelium. There is n incresed nucler cytoplsmic rtio, nisocytosis, nd loss of nucler polrity. Severl mitoses re present throughout the upper two thirds of the epithelium. Key points rchitecture chnges in the epithelium re reltively unequivocl nd re disordered throughout ll cellulr lyers (Fig. 3.6). Cytologicl exmintion of n HSIL cnnot e s precise, nd cytologist reporting HSIL will proly descrie sl cells tht hve risen to the intermedite or superficil lyers, which re norml with enlrged nuclei nd reduced cytoplsm, s in Fig. 3.6. However, the histologicl dignosis is not roust in the middle grde, nd the ctegory of CIN2 or HSIL- IN2 contins some cses where the virus is trnsforming nd the risk of progression is rel nd some cses where the virus is prolifertive nd not trnsforming nd the risk of progression to cncer is very smll. Morphologicl exmintion of tissue iopsies from CIN2 cses is not relile, nd pthologists will often not gree. Some will cll the cse CIN3, nd some will cll it CIN1. In this sitution, moleculr iology tests cn resolve the disprity. To pprecite how moleculr iology tests cn help, it is necessry to understnd little out the iology of oncogenic HPV nd its effect on squmous epithelium (see Chpter 4). Oncogenic (or high-risk) HPV is n extremely common infection in helthy sexully ctive women of reproductive ge. Cervicl cncer is very rre outcome of oncogenic HPV infection ut does not occur in its sence. Up to 80% of women will hrour oncogenic HPV during their reproductive life, ut only 1 in 10 000 or fewer will develop cervicl cncer. A positive high-risk HPV test does not imply cncer, precncer, or even n ctive infection. Cytologicl, colposcopic, nd histologicl recognition of cervicl cncer precursor sttes re ll imperfect, ecuse of their innte sujectivity. Chpter 3. Squmous intrepithelil lesions: cytology histology correltion 27