Are retroviruses involved in the aetiology of human breast cancer?

To further investigate the possibility for retroviral involvement in the etiology of human breast cancer we processed peripheral blood monocytes and malignant breast tissue biopsies from 10 patients with breast cancer (infiltrating ductal carcinoma or infiltrating lobular carcinoma; ages 40–80 years) and 20 normal healthy women (with no evidence or family history of breast cancer; 10 age-matched controls and 10 women age 22–27 years) for the assay of the retroviral enzyme, reverse transcriptase, using an ELISA and for electron microscopy examination for the detection of retroviral-like particles. Reverse transcriptase activity was detected in 5 out of 10 samples of monocyte culture medium and in 1 out of 10 of the malignant tissue biopsies from the patients with breast cancer. In contrast, reverse transcriptase was not detected in the culture medium of the monocytes from any of the control subjects. Electron microscopy did not reveal the presence of any retroviral-like particles in any sample of monocyte culture medium or in any of the malignant or normal breast tissue biopsies. Despite evidence for the presence of reverse transcriptase in a subsample of the monocyte culture medium and breast tissue biopsies from the cohort of breast cancer patients who participated in this study, the role of retroviruses in human breast cancer remains unclear.