Second cancer following lymphatic and hematopoietic cancers in Denmark, 1943-80.

In Denmark, approximately 5% of all malignant neoplasms occur within the lymphatic and hematopoietic tissues. Between 1943 and 1980, 23,367 persons with these diseases fulfilled the criteria for entering the study. The risk of developing a second primary cancer was significantly increased only after Hodgkin's disease [relative risk (RR) = 1.6], whereas no increase was found after non-Hodgkin's lymphoma [(NHL); RR = 1.0] or leukemia (RR = 1.1), and a significant deficit occurred after multiple myeloma (RR = 0.8). All initial cancer sites showed a higher incidence of second primary cancers among males than females. Significant elevated risks for acute non-lymphocytic leukemia occurred after Hodgkin's disease (RR = 17), NHL (3.8), and multiple myeloma (9.1). Among persons initially diagnosed with leukemia, NHL was significantly elevated (RR = 2.6). However, these RR should be regarded as minimum figures due to the likelihood of serious underreporting of second primary hematologic cancers in Denmark. The secondary leukemias were likely induced by the treatment of the first primary cancer (chemotherapy, radiotherapy), but common etiologies, misclassification, or progression of the initial cancer cannot be ruled out entirely. Other second primary cancers found to be above expectation following Hodgkin's disease were cancers of the pancreas, lung, and urinary bladder. The risk for bladder cancer increased with time, which suggested a causal relation to radiation or chemotherapy, or both. Cancers of the colon and rectum following NHL and female breast cancer following leukemia occurred below expectation and remain unexplained.