Non-Hodgkin's lymphoma in women with breast cancer.

The purpose of this study was to describe a series of patients with breast cancer and non-Hodgkin's lymphoma and to determine the usual sequence of the diagnoses. Therapy for both neoplasms and its relationship to the development of the second neoplasm were also evaluated.Patients were identified primarily from cancer registries at various institutions. The observed proportion of women diagnosed with breast cancer first, after, or simultaneously with non-Hodgkin's lymphoma was compared with the expected proportion by employing New York State and Surveillance, Epidemiology, and End Results program cancer incidence rates.The expected number of lymphoma cases that were diagnosed after or simultaneously with breast cancer was 31.6 (New York state data) to 39.1 (New York State and Surveillance, Epidemiology, and End Results data), and 78 such cases were identified from a total group of 87 (P < or = .001). There was no evidence that in this study, lymphoma as a second neoplasm was therapy induced.Anecdotal case reports suggest a relationship between breast cancer and non-Hodgkin's lymphoma. Mouse mammary tumor virus induces breast cancer and, in some circumstances, lymphoma in mice. The mouse mammary tumor virus ENV gene has been identified in approximately one third of human breast cancers. Women with both breast cancer and lymphoma are diagnosed first with breast cancer or simultaneously with both cancers more frequently than expected, and the lymphoma is not therapy induced. In some women with both breast cancer and lymphoma, the two neoplasms may have a common etiology, perhaps viral.