Antecedent therapy versus detection bias as causes of neoplastic multimorbidity.

Neoplastic multimorbidity occurs when a patient is found to have a second primary cancer after the occurrence of a first. The phenomenon may be the result of aging, chance, or other specific causes, but in recent years, the radio- or chemotherapy administered for the first cancer has regularly been suspected as a possible cause of the second. A commonly disregarded alternative explanation, however, is that the second cancers were clinically "silent" discoveries found because of increased diagnostic detection procedures in patients known to have a first cancer. Such patients are more likely to receive intensive surveillance and technologic testing than the general population often used as a control group. In 43 recent reports of neoplastic multimorbidity, however, only five mentioned the problem of detection bias, and only one tried to eliminate it by using a suitable analytic comparison. Unless adequate analytic precautions are taken, antineoplastic therapy may be falsely accused of being carcinogenic.