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Increased risk of male breast cancer seen in prostate cancer patients

Last Updated: 2003-03-25 13:08:01 -0400 (Reuters Health)

NEW YORK (Reuters Health) - Men diagnosed with prostate cancer are slightly more likely than other men to develop a second primary cancer, according to a new report.

The increased risk may simply stem from greater surveillance in men diagnosed with this malignancy. However, for at least one malignancy--male breast cancer--there does appear to be a significant association with prostate cancer.

The current findings run counter to previous reports showing that the overall risk of a second primary cancer is decreased after a diagnosis of prostate cancer. Still, a few reports have suggested that the risk of certain malignancies, such as bladder and kidney cancer, is increased after a prostate cancer diagnosis.

To further evaluate the link between prostate cancer and second primary malignancies, Dr. Camilla Thellenberg and colleagues, from Umea University in Sweden, analyzed data from all prostate cancer cases that were entered in the Swedish Cancer Registry from 1958 to 1996. A total of 135,713 cases were included in the study.

The researchers' findings are published in the April issue of The Journal of Urology.

In the study group, a total of 10,536 second primary cancers were identified. For a comparably sized group in the general population, 8984 cancers would have been expected. This equates to a standardized incidence ratio of 1.17 in men with prostate cancer.

Further analysis revealed that the elevated overall risk was limited to the 6 months following prostate cancer diagnosis. Beyond that point, prostate cancer was actually associated with a decreased risk of other malignancies. Taken together, these findings suggest that much of the increased risk was due to surveillance bias.

The researchers identified several tumor types that were more common after a prostate cancer diagnosis. Male breast cancer (SIR = 2.01) and small intestine tumors (SIR = 1.39) were both more likely in prostate cancer patients than in the general population. Other tumors linked to prostate cancer included endocrine tumors and skin melanoma.

There are two possible explanations for the link between prostate cancer and male breast cancer, the authors note. First, the mammary tumor may not have actually been a primary breast cancer, but rather a metastasis from the prostate cancer. Second, and a more likely explanation, is that the hormonal therapy used to treat prostate cancer induced the breast cancer.

"To our knowledge," the associations with male breast cancer and small intestine tumors "have not been reported previously, and they warrant more study," the investigators note.

J Urol 2003;169:1345-1348.

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