Head trauma and exposure to prolactin-elevating drugs as risk factors for male breast cancer.

On the basis of information obtained from a population-based cancer registry in Sweden, male patients with breast cancer (n = 95) were found to have experienced significantly more brain concussions and skull fractures than male patients with lung cancer (n = 383) or malignant lymphoma (n = 69). Other risk factors significantly associated with breast cancer among men were drug treatment associated with prolactin elevations, radiation treatment, family history of breast cancer among first-degree relatives, a history of gynecomastia, gonadal injury, and treatment for inguinal hernias. The results confirm some previously described risk factors for male breast cancer and suggest that events elevating plasma prolactin (e.g., drugs, brain concussions, and skull fractures) and events predisposing for inguinal hernias may be new risk factors for the disease. Using hospital charts is likely to underestimate exposure for different risk factors; therefore, the results need to be confirmed in studies that directly retrieve information. However, such studies are difficult or impossible to undertake in most countries because the disease is so rare.