At
Jose Eluf Neto
Etiological studies - human papillomavirus
and cervical cancer
Departamento
de Medicina Preventiva -
Faculdade
de
Medicina
da USP
S in c e z u r H a u s e n (1 9 7 6 ) d re w a tte n tio n to p a p ilo m a v iru s a s a p o s s ib le a g e n t fo r g e n ita l c a n c e r, im p re s s iv e e x p e rim e n -ta l d a -ta h a v e b e e n a c c u m u la te d s u p p o rtin g a n e tio lo g ic a l ro le fo r h u m a n p a p illo m a v iru s (H P V ) in th e p a th o g e n e s is o f c e r-v ic a l c a n c e r. E a rly e p id e m io lo g ic a l s tu d ie s in v e s tig a tin g th e re la tio n b e tw e e n H P V a n d c e rv ic a l n e o p la s ia fo u n d s tro n g a s s o c ia tio n s . T h e s e s tu d ie s , h o w e v e r, p re s e n te d im p o rta n t m e th o d o g ic a l p ro b le m s s u c h a s s m a ll s a m p le s iz e , b ia s e d s e -le c tio n o f s tu d y s u b je c ts , d iffe re n t c e rv ic a l s a m p lin g m e th -o d s f-o r c a s e s a n d c -o n tr-o ls , a n d little o r n o c o n tro l fo r c o n -fo u n d in g . U n e x p c te d fin d in g s re p o rte d fro m c a re fu lly d e -s ig n e d -s tu d ie -s w e re a ttrib u te d to th e u s e o f filte r in s itu h y -b rid iz a tio n (F IS H ), n o w re g a rd e d a s a te c h n iq u e w ith lo w a c c u ra c y . A re lia b le a n d s e n s itiv e H P V d e te c tio n s tra te g y b a s e d o n p o ly m e ra s e c h a in re a c tio n (P C R ), re c e n tly d e v e l-o p e d , is n l-o w c l-o n s id e re d th e te c h n iq u e o f c h o ic e fo r e p id e -m io lo g ic a l s tu d ie s . .
In d e v e lo p in g c o u n trie s c a n c e r o f th e c e rv ix is th e le a -d in g c a n c e r e v e n w h e n s i te s c o m m o n to b o th s e x e s a re c o m -b in e d . A h o s p ita l--b a s e d c a s e -c o n tro l s tu d y w a s u n d e rta k e n to e x a m in e th e e tio lo g ic a l ro le o f H P V in th e d e v e lo p m e n t o f in v a s iv e c e rv ic a l c a n c e r in S a o P a u lo , B ra z il, u s in g P C R .
W o m e n w ith a d ia g n o s is o f in v a s iv e c e rv ic a l c a n c e r a n d w o m e n s e le c te d a s c o n tro ls w e re re c ru ite d fro m s e v e n h o s p i-ta ls o fS a o P a u lo c ity , b e tw e e n J u n e 1 9 9 0 a n d J u n e 1 9 9 1 . T h e c a s e s w e re w o m e n le s s th a n 8 0 y e a rs o ld , w ith d ia g n o s is c o n -firm e d b y b io p s y a n d w h o h a d h a d n o p re v io u s tre a tm e n t fo r th e d is e a s e . C o n tro ls e n ro lle d fro m h o s p ita ls w e re th e c a s e s w e re c ru ite d w e re a g e -fre q u e n c y . m a tc h e d to th e c a s e s . P a -tie n ts a d m itte d fo r tre a tm e n t o f a g y n e c o lo g ic a l c o n d itio n o r w h o h a d h a d a h y s te re c to m y c o ris a tio n w e re in e le g ib le a s c o n -tro ls a s w e re th o s e w ith d is e a s e s a s s o c ia te d w ith k n o w n ris k fa c to rs fo r c e rv ic a l n e o p la s ia . E v id e n c e o f a g y n e c o lo g ic a l o r c y to lo g ic a l a b n o rm a lity d e te c te d o n e x a m in a tio n a fte r re c ru it-m e n t w a s n o t a c rite rio n fo r e x c lu s io n .
T w o h u n d re d a n d s ix w o m e n w ith in v a s iv e c e rv ic a l c a n
-e -e l' a n d 2 3 8 c o n tro ls w e re e lig ib le fo r in v e s tig a tio n ; 1 9 9 (9 6 .6 % ) a n d 2 2 5 (9 4 .5 % ), re s p e c tiv e ly , w e re in te rv ie w e d . T h e c o n tro ls w e re s e le c te d fro m a w id e ra n g e o f d ia g n o s tic c a te -g o rie s . S tu d y s u b je c ts w e re in te rv ie w e d p riv a te ly in th e h o s -p ita l u s in g a s ta n d a rd iz e d q u e s tio n n a ire . A ll s tu d y h a d a p e l-v ic e x a m in a tio n p e rfo rm e d b y a g y n a c o lo g is t w h e n e x fo li-a te d c e lls fo r c y to lo g ic li-a l e x a m in a tio n a n d fo r H P V a n a ly s is w e re c o lle c te d . O n e c o n tro l (0 .5 % ) h a d c y to lo g c a l e v id e n c e o f lo w -g ra d e s q u a m o u s in tra e p ith e lia l le s io n ; s h e w a s re ta in e d in th e s tu d y .
A P C R te c h n iq u e w a s u s e d to a n a ly s e H P V D N A in c e rv ic a l s p e c im e n ts c o lle c te d w ith s p a tu la a n d b ru s h . D u rin g s a m p le p re p a ra tio n c a re w a s ta k e n to a v o id c o n ta m in a tio n ; th e e q u ip a m e n t u s e d w a s d is p o s a b le . W h e n th e s tu d y w a s c o m p le te d , th e m a te ria l w a s s e n t to th e D e p a rtm e n t o f P a -th o lo g y , F re e U n iv e rs ity H o s p ita l, A m s te rd a m . H P V d e te c -tio n w a s p e rfo rm e d d ire c tly o n c ru d e c e ll s u s p e n s io n s w ith -o u t k n -o w le d g e o f th e c a s e /c o n tro l s ta tu s .
T o e s tim a te th e ris k o f c e rv ic a l c a n c e r a s s o c ia te d w ith s e le c te d fa c to rs , o d d s ra tio s (O R ) a n d 9 5 p e r c e n t c o n fid e n c e in te rv a ls (9 5 % C l) w e re c a lc u la te d u s in g u n c o n d i~ io n a l lo -g is tic re -g re s s io n a n a ly s is . P o te n tia l c o n fo u n d in -g v a ria b le s a n d in te ra c tio n s w ith th e fa c to rs o f in te re s t w e re e x a m in e d . S ta -tis tic a l s ig n ific a n c e w a s a s s e s s e d u s in g th e lik e ly h o o d ra tio te s t. T e s ts fo r tre n d w e re m a d e b y c a te g o riz in g th e e x p o s u re v a ria b le s a n d e n te rin g th e s c o re s a s c o n tin u o u s .
H P V D N A w a s d e te c te d in 1 5 7 (8 4 % ) o f th e 1 8 6 c a s e s a n d i~ 3 4 (1 7 % ) o f th e 1 9 6 c o n tro ls w ith c e rv ic a l s p e c im e n ts (e x fo lia te d c e lls ) in w h ic h th e B -g lo b in g e n e w a s a m p life d . C e rv ic a l s p e c im e n ts o b ta in e d b y b io p s y w e re te s te d in 1 6 o f th e 2 9 c a s e s w h o s e s m e a r w a s n e g a tiv e fo r H P V D N A ; in e ig h t (5 0 % ) o f th e m H P V D N A w a s d e te c te d . T h e o d d s ra -tio s o f c e rv ic a l c a n c e r a s s o c ia te d w ith d iffe re n t ty p e s o f H P V D N A h a rd ly c h a n g e d o fte r a llo w in g fo r n u m b e r o f s e x u a l p a rt-n e rs a rt-n d a g e a t firs t irt-n te rc o u rs e . T h e m o s t c o m m o n ty p e o f H P V a m o n g c a s e s w a s H P V 1 6 w h e re a s a m o n g c o n tro ls , u n
dentified H P V types w ere the m ost frequent. G rouping high-risk types (H P V 16/18/31/33), alm ost 66% of the cases w ere positive com pared to only six-percent of the controls. T he adjusted odds ratio of cervical cancer associated w ith these types w as 69.7 (95% C l 28.7-169.6).
Interactions betw een detection of H P V D N A and seve-ral factors w ere investigated. A ge w as the only variable suggestng a possible interaction w ith H P V . T he risk w as higher am ong older w om en than am ong younger, but the term for interaction w as not significant (p = 0.09). In the analisys of interaction entering H P V types (negative, unidentified and 16/18/31/33) instead of negative/positive, the enhanced ef-fect in older w om en w as essentialy restricted to unidentified H P V types and the term for interaction w as statistically sig-nificant (p=0.007).
T he risk of cervical cancer associated w ith presence of the H P V types 16/18/31/33 w as very high. R isks of such m agnitude are rarely found in epidem iological studies, being very higher than those found w ith hepatitis B virus for hepa-tocellular carcinom a, T he estim ates rem ained practically un-changed after adjustm ent for m easures of sexual behaviour, in accordance w ith the current proposed m odel for cancer of the cervix.
A higher risk of cervical cancer associated w ith H P V D N A detection w as found am ong older w om en. T he interac-tion w as m ainly betw een age and unidentified types. S ince unidentified types should include H P V s associated w ith low er risk of cervical cancer than H P V s 16,18,31 and 33, it m ight suggest that unidentified types need longer to achieve m alig-nant conversion. T his finding deserves confirm ation.
W ith a case-control design one cannot be sure w hether the H P V infection preceded or postdated the disease. T he 11igherprevalence ofH P V in w om en w ithless advanced stages found in this study and by other suggests that H P V did not
follow the m alignant conversion. In addition, results from C o-lom bia and S pain show ed sim ilar proportions of H P V -D N A positivity in w om en w ith cervical cancer regardless w hether they w ere currently sexually active or w hether their last sexual intercourse w as m ore than 10 or even 20 years previously. It m ight be easier to detect H P V in infected cancer cells rather than in infected non-m alignant cells. A s density and sam pling distribution for specim ens of exfoliated cells m ay differ be-tw een cases and controls, it has been speculated that m isclassification in detecting H P V D N A could be low er am ong cases than am ong controls. N o clear evidence for in-creased susceptibility or higher detection of H P V D N A in m alignant cells how ever, has so far been dem onstrated.
P roving that a virus causes cancer presents som e dificulties. O nly a sm all proportion of individuals w ho carry the virus (often asyptom atic) w ill develop the disease. L a-tency betw een prim ary infection and cancer appearence usu-ally takes several years of decades. A non-trivial proportion of w om en w ith norm al cytology but w ith H P V detected indi-cates that H P V is not a sufficient cause. C onversely, a certain percentage, albeit sm all, of w om en w ith cervical cancer in w hom H P V D N A cannot be detected suggests that this virus is not a necessary cause. It is a m atter of concern that H P V types related to anogenital cancer have also been detected in m any other diverse tum ors such as laryngeal carcinom a, uri-nary bladder carcinom a, prostate carcinom a, esophageal squa-m ous-cell carcinosqua-m a, oral cancer and K aposi's sarcom a.
T his case-control study w as hospital-based. H ow ever, care w as taken to select controls w ith a w ide range of diag-noses and cases w ere restricted to invasive stages. T he ex-perim ental evidence for the m alignant potential of H P V and the very high risks fopnd in this study, particularly in relation to H P V types 16,18,31 and 33, futher im plicates this virus in the etiology of cervical cancer.
