Any im­mune loss in­creases can­cer risk

The Weekend Australian - Travel - - Health - Adam Cress­well Health ed­i­tor

HAV­ING HIV in­creases the risk of de­vel­op­ing 20 dif­fer­ent types of can­cer — not just the three types that have been as­so­ci­ated with the virus to date, ac­cord­ing to Aus­tralian re­search. The find­ings, pub­lished last week in the UK jour­nal The Lancet in the run-up to an in­ter­na­tional AIDS con­fer­ence in Syd­ney, will have ‘‘ huge im­pli­ca­tions’’ for the fu­ture care of HIV-in­fected pa­tients, ac­cord­ing to an ac­com­pa­ny­ing edi­to­rial in the jour­nal.

But the study (2007;370:59-67) is also likely to change un­der­stand­ing of the role of the im­mune sys­tem in fight­ing can­cer, and not just for HIV-in­fected pa­tients.

The study, by pro­fes­sion­als from the Univer­sity of NSW, re­viewed the re­sults of 12 pre­vi­ous tri­als. Seven of those looked at can­cer rates in a to­tal of nearly half a mil­lion pa­tients with HIV, while the five other stud­ies ex­am­ined can­cer rates in 31,977 kid­ney trans­plant re­cip­i­ents.

Trans­plant re­cip­i­ents have to take drugs that sup­press the im­mune sys­tem to pre­vent their bod­ies re­ject­ing the trans­planted or­gan, while peo­ple in­fected with HIV also have im­paired im­mune func­tion as a re­sult of their in­fec­tion, as the HIV virus par­tic­u­larly tar­gets im­mune cells.

Pre­vi­ous at­tempts to ex­am­ine the ef­fect of im­mune sys­tem com­pro­mise on can­cer rates have suf­fered from the rel­a­tive scarcity of trans­plant pa­tients — the main cir­cum­stance that led to im­paired im­mu­nity be­fore the AIDS era — which made it dif­fi­cult to gather enough study sub­jects for the re­sults to be sta­tis­ti­cally mean­ing­ful.

Pre­vi­ously, AIDS — the end-stage of HIV in­fec­tion, caused by op­por­tunis­tic in­fec­tions over­whelm­ing the body’s run-down im­mune de­fences — has only been as­so­ci­ated with three can­cers: non-Hodgkin’s lym­phoma, cer­vi­cal can­cer and Ka­posi’s sar­coma.

But when the UNSW au­thors com­bined the pre­vi­ous study data, they found that rates of 20 out of the 28 can­cers stud­ied were sig­nif­i­cantly in­creased in both the trans­plant and HIV-in­fected groups.

‘‘ We be­lieve that the strik­ing sim­i­lar­ity in pat­terns of in­creased can­cer risk that we have shown in­di­cates that im­mune de­fi­ciency is the prob­a­ble ex­pla­na­tion for the in­creased can­cer risk,’’ they wrote. ‘‘ The in­creased rates of can­cers we have found . . . sug­gests a broader than pre­vi­ously ap­pre­ci­ated role for the im­mune sys­tem in the pre­ven­tion of can­cers re­lated to in­fec­tion. If im­mune de­fi­ciency is as­so­ci­ated with such a broad range of can­cer types, then can­cer is likely to be­come an in­creas­ingly im­por­tant cause of mor­bid­ity in peo­ple with HIV/AIDS.’’

Lead au­thor pro­fes­sor Andrew Grulich, head of the HIV epi­demi­ol­ogy and pre­ven­tion pro­gram at UNSW’s Na­tional Cen­tre in HIV Epi­demi­ol­ogy and Clin­i­cal Re­search, said a strength of the study was that the two groups it com­pared had lit­tle in com­mon other than their im­mune com­pro­mise.

Can­cers that af­fected both groups at higher rates in­cluded Hodgkin’s lym­phoma — as­so­ci­ated with the Ep­stein Barr virus — which is 11 times more likely in HIV-in­fected pa­tients than in the gen­eral pop­u­la­tion, and four times more likely in trans­plant pa­tients.

A range of other can­cers as­so­ci­ated with the hu­man pa­pil­lo­mavirus, such as cer­vi­cal can­cer, and can­cers of the mouth, pe­nis and anus, were also sig­nif­i­cantly more com­mon across both groups.

‘‘ In other can­cers, which are not linked with viruses, such as breast and prostate can­cer, both groups had sim­i­lar rates to the gen­eral pop­u­la­tion,’’ Pro­fes­sor Grulich said. ‘‘ This ev­i­dence sug­gests that im­mune de­fi­ciency is as­so­ci­ated with risk of can­cer, and this sug­gests we need to main­tain peo­ple’s im­mune sys­tems at a higher level. That might mean putting HIV pa­tients on anti-retro­vi­ral drugs ear­lier than is cur­rently the case.’’

The study’s re­sults also sug­gest that CD4 counts — a mea­sure of how many of one type of im­mune cell tar­geted by HIV are cir­cu­lat­ing in a pa­tient’s blood — is an im­per­fect mea­sure of im­mune func­tion.

CD4 counts are of­ten used to gauge ef­fec­tive­ness of anti-HIV ther­apy, and when an in­fected pa­tient should start us­ing it. But pre­vi­ous stud­ies have shown a poor as­so­ci­a­tion be­tween CD4 counts at the point when a pa­tient is di­ag­nosed with AIDS and can­cer rates, sug­gest­ing other im­mune sys­tems are more im­por­tant.

The Lancet de­voted its en­tire July 6 is­sue to HIV, ahead of the In­ter­na­tional AIDS So­ci­ety Con­fer­ence, which is ex­pected to at­tract 5000 del­e­gates and will be held in Syd­ney from July 22 to 25.

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