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Simian virus in polio shots tied to cancer

Two stud­ies sup­port wide­ly dis­put­ed the­o­ry

by William Carlsen
San Fran­cis­co Chron­i­cle

Sci­en­tists have found traces of a mon­key virus that con­t­a­m­i­nat­ed the polio vac­cine in the 1950s in a com­mon form of high­ly malig­nant human can­cer that has mys­te­ri­ous­ly dou­bled in inci­dence over the past 30 years.

Two stud­ies, pub­lished yes­ter­day in the British jour­nal Lancet, found a link between the virus, called SV40, and non-Hodgk­in’s lym­phomas, a dis­or­der ranked fourth or fifth among can­cer deaths in the Unit­ed States among women and men, respec­tive­ly.

Results sug­gest that the virus may play a much wider role in can­cer than pre­vi­ous­ly sus­pect­ed.

“No obvi­ous risk fac­tors have emerged for non-Hodgk­in’s lym­phoma in the gen­er­al pop­u­la­tion, but a viral cause has been pos­tu­lat­ed,” said a group of eight researchers at Bay­lor Col­lege of Med­i­cine in Texas led by Dr. Janet Butel. “This find­ing sheds new light on the pos­si­ble gen­e­sis of (this) impor­tant group of malig­nant dis­or­ders.”

The sci­en­tists added that their find­ings may also offer hope for new ther­a­pies for the malig­nan­cies.

The Salk polio vac­cine, admin­is­tered by injec­tion in the Unit­ed States and world­wide from 1955 through 1963, was grown on minced kid­ney tis­sue from rhe­sus mon­keys.

At the time, the man­u­fac­tur­ing process was con­sid­ered safe. But in 1960, it was dis­cov­ered that large batch­es of the vac­cine were con­t­a­m­i­nat­ed with the simi­an virus lat­er named SV40. An esti­mat­ed 90 mil­lion Amer­i­cans received Salk vac­cine injec­tions and as many as 30 mil­lion were exposed to the virus.

In lab­o­ra­to­ry tests, ham­sters inject­ed with SV40 devel­oped a vari­ety of malig­nant tumors, but ear­ly gov­ern­ment stud­ies indi­cat­ed that the virus appeared to have no neg­a­tive effect in humans who had been exposed.

That view began to change in the 1990s when DNA detec­tion tech­niques became much more refined and evi­dence of the virus start­ed show­ing up in human tumors.

The group includ­ed rare brain, bone and lung-relat­ed can­cers called mesothe­liomas.

Oth­er research has also turned up SV40 in tumors of chil­dren and adults born after the con­t­a­m­i­nat­ed vac­cine was tak­en off the mar­ket in 1963, lead­ing to the still-unsolved mys­tery of how the virus is being trans­mit­ted.


Yes­ter­day’s reports indi­cate that SV40 may be involved in a much broad­er group of human can­cers, play­ing a pos­si­ble role in near­ly half of the 55,000 new cas­es of non-Hodgk­in’s lym­phoma diag­nosed annu­al­ly.

The can­cer, which can be high­ly aggres­sive, has been asso­ci­at­ed with HIV- pos­i­tive patients, and it was thought that the sup­pres­sion of the immune sys­tem in these patients may have had a con­nec­tion with the dra­mat­ic increase in lym­phomas since 1970.

The new stud­ies exam­ined lym­phomas from HIV-pos­i­tive and ‑neg­a­tive patients.

Results sug­gest­ed that both groups had either about the same lev­el of SV40 DNA frag­ments, or that the HIV-neg­a­tive sam­ples had a greater inci­dence.

The sec­ond group of researchers were at the Fred Hutchin­son Can­cer Research Cen­ter in Seat­tle and the Uni­ver­si­ty of Texas South­west­ern Med­ical Cen­ter in Dal­las.

Remark­ably, both groups of researchers using slight­ly dif­fer­ent detec­tion tech­niques came up with almost iden­ti­cal results: SV40 frag­ments were found in 42 per­cent of 154 lym­phomas sam­pled in one study, while the oth­er found 43 per­cent in 68 cas­es.

No virus was detect­ed by either study in non­ma­lig­nant lym­phoid sam­ples and oth­er can­cers used as con­trols.

A Chron­i­cle inves­ti­ga­tion report­ed last year that there is a heat­ed con­tro­ver­sy sur­round­ing detec­tion of SV40 and that most U.S. gov­ern­men­t’s stud­ies over the past decade have debunked the the­o­ry that SV40 is caus­ing human can­cer or is even present in tumors.

But The Chron­i­cle found that more than 60 stud­ies from 30 lab­o­ra­to­ries around the world have report­ed detec­tions of the virus in human malig­nan­cies.

“I’ve been in meet­ings where peo­ple say there is noth­ing to it,” said Dr. Jay A. Levy, a renowned virol­o­gist at the Uni­ver­si­ty of Cal­i­for­nia at San Fran­cis­co. “That atti­tude is wrong.”

Levy said he had care­ful­ly reviewed the papers pub­lished yes­ter­day and was impressed with the research. “You just can’t walk away from it,” he said, not­ing that the asso­ci­a­tion found was very strong.

“But there is still quite a dif­fer­ence between asso­ci­a­tion and cau­sa­tion,” he added, “and prov­ing cau­sa­tion is very dif­fi­cult.”


Dr. Adi Gaz­dar of the Uni­ver­si­ty of Texas, who led the sec­ond study, said yes­ter­day that the “data is very, very sol­id.” He said it had to be more than coin­ci­dence that the four types of tumors found in ham­sters after injec­tion with SV40 — brain, bone, mesothe­lioma and lym­phomas — are now exact­ly the same tumor types in humans found with detectable lev­els of SV40.

“The chances are 10 mil­lion to 1 it is a coin­ci­dence,” he said.

Evi­dence of how the virus works in tumors is grow­ing as research shows that pro­teins from SV40 have a pow­er­ful effect in turn­ing off tumor sup­pres­sor genes in humans.

Gaz­dar and the oth­er researchers said that the recent SV40 dis­cov­er­ies also could help lead to effec­tive can­cer treat­ment, by using SV40 as a tar­get for ther­a­pies.

“A vac­cine tar­get­ing SV40 in mesothe­lioma is now being devel­oped,” he said. “But it’s still only a poten­tial ther­a­py, and we don’t know if it will work yet.”

He said that U.S. offi­cials have all but ignored the SV40 detec­tions and that gov­ern­ment fund­ing and sup­port for research has been nonex­is­tent.

One rea­son giv­en by Gaz­dar and oth­er sci­en­tists is that the gov­ern­ment is wor­ried about its role in pro­mot­ing polio vac­ci­na­tion cam­paigns in the 1950s.

“And maybe it’s because the first SV40-relat­ed can­cers that were dis­cov­ered were such rare ones,” Gaz­dar said. “But you can’t ignore lym­phoma; it’s too wide­spread and too impor­tant a can­cer. Jack­ie Kennedy and a lot of oth­er well-known peo­ple have died from it.”


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