The sudden rise in the number of deaths from non-Hodgkin's lymphoma may be linked to the polio vaccine given to children in the USA until 1963.
Researchers have found the polyomavirus known as simian virus 40 (SV40) in a large number of lymphoma sufferers - the same virus that was in the contaminated batch of polio vaccines.
The vaccine was prepared in rhesus monkey kidney cells, but some of the animals were infected with the SV40, which was then passed on to the vaccinated children. In all, millions of children from all 50 states were exposed to the virus from 1955 until 1963, when the vaccine was finally withdrawn.
The number of non-Hodgkin's lymphoma cases began to leap markedly in 1970 and now, 55,000 new cases are reported every year in the US. It has also been closely linked to HIV-1-infected patients. Of all types of cancer, it is now the fourth major killer among women, and fifth among men.
A study team from the Baylor College of Medicine in Houston, Texas, analysed the cancerous lymphomas from 76 HIV-1-infected and 78 non-infected patients as well as non-malignant lymphoid samples from 79 HIV-1-positive and 107 HIV-1-negative patients who had no tumours. Samples of colon and breast cancers were also taken from 54 patients serving as controls.
SV40 was found in 64 - 42 per cent - of the 154 patients with the cancer, irrespective of whether they were HIV-positive or not. The virus was not found in any of the patients who had non-malignant tumours nor in any of the other cancer controls.
Researchers found that the amount of contaminated virus in the vaccines varied from state to state, which may explain the uneven distribution of the cancer.
The legacy of the contaminated vaccines may not end with the generation that received it. Studies have found that the virus is appearing in children born after 1963, which suggests that it is being transmitted between humans, although nobody seems to be clear on how this is happening (Lancet, 2002; 359: 817-23).