Observations on the proposed relationship between infection burden and early malignancy in developing countries (e.g., India).

Sastry and Parikh [Med. Hypotheses 60(4) (2003) 573] have recently sought an explanation for the fact that the occurrence of a particular cancer in populations in a developing country such as India takes place at a younger age (about one decade) than in populations in Western countries. They have hypothesized that a higher infectious burden in India gives rise to repeated cell divisions leading to early senescence of immune cells, and, thence their reduced ability for immune surveillance against cancer, resulting in earlier onset of cancer. The analysis presented here points out to some difficulties with this interpretation, both on empirical and theoretical grounds. The reduced surveillance ability, caused by higher infectious burden, of the immune cells postulated by Sastry and Parikh [loc. cit.] would also mean that populations in India should suffer higher incidence of cancer, as compared to people in Western countries; the empirical data show that, in fact, quite the opposite is true - in the present communication shows that for many common cancers, typical cities in India show the lowest incidence. Theoretically, it is postulated here that repeated heavy infections in India, in fact, challenge the immune system, particularly the adaptive immune system and create an immunological memory: this trains and strengthens the immune system against the future battles. Also it is shown that the shortening of the telomeric cap by repeated cell divisions caused by heavy infectious attacks, as argued by Sastry and Parikh [loc. cit.], is not the cause of earlier onset of cancers among Indians; in fact, when telomeric caps become shortened to a critical point, a danger signal is generated arresting the cell cycle - thus, it provides a fundamental mechanism for ordering the cell to cease proliferation. It is suggested that the root of occurrence of cancers at an earlier age in India perhaps lies in the accumulation of mutations at an earlier age among Indians who do develop cancers; the factors responsible for these accelerated mutations are not clear at the present time and need further investigation.