Is Natural Infection with M. tuberculosis Protective against Cancer?

In order to investigate the effect of natural infection with M. tuberculosis on cancer incidence, a case-control study was undertaken on 108 recently diagnosed cancer cases (all sites) and 317 controls. After removal of cancer cases or controls considered immunoincompetent (25% and 17% respectively), the remaining subjects were tested by intradermal injection of tuberculin (5 I.U.). Results were compared separately for each sex. It was observed that the proportion of tuberculin-negative subjects was higher in cancer patients than in controls within each sex (males 31.3% vs 20.1%, females: 59.2% vs 37.3%) the difference in females being statistically significant (p < 0.02). Odds ratio for negative tuberculin test was 1.80 and 2.44 for males and females respectively. The results are discussed on the basis of cell-mediated immunity produced by infection with M. tuberculosis and its relations with tumor growth.