In recent years, health officials have pushed aggressively to include more women in clinical trials of new drugs. Gone is the ban that once excluded women of childbearing age from participating in studies. Even scientists who work with animals are now encouraged to include mice and rats of both sexes.

But when it comes to breast cancer, it is men who get short shrift. They are often excluded from clinical trials of new treatments. When new breast cancer drugs come to market, there is little data to indicate whether they are safe or effective in men. Some new drugs are approved only for women.

The disease is extremely rare in men, who account for fewer than 1 percent of breast cancer cases. Nonetheless, the Food and Drug Administration is calling on researchers to include male patients in clinical trials of breast cancer treatments, even if the studies are unlikely to enroll more than a handful of male patients.

The guidance is a draft recommendation now open to public comment. Some breast cancer specialists called it a long overdue step.