Bias can arise where one sex is the normative standard in medical research for a particular disease.
Such is the case with male breast cancer. Women are 100 times more susceptible to breast cancer than are men, and men often do not think of themselves as having breasts, so research on and therapy for this cancer has focused exclusively on its occurrence in women. A lump in a man's breast may be reported late, or not recognized due to lack of expectation of, or experience with its occurrence in men, or may remain untreated or be treated inappropriately. The survival rate for men with breast cancer is lower than for women.
Men with breast cancer find breast cancer support groups unhelpful as they tend to revolve around women's concerns; the loss of a breast has sexual implications for a woman that it may not have for a man, and men do not need breast reconstruction. Waiting rooms for breast cancer treatment and diagnosis tend to be for women only, and so examinations for men must be scheduled when no women are around, which reinforces the sense of loneliness a male cancer patient feels.
Women's health issues were underrated for a long time by the medical profession. The emphasis on women's breast cancer, although unfortunately neglectful of the male risk of cancer, indicates at least that gender bias in medicine is being addressed.