It’s day 8 of National Breast Cancer Awareness Month! Breast cancer is widely considered to be a disease of biological females (e.g. cis women, intersex people), though cis men, trans men who forgo top surgery and trans women can develop breast cancer, as can non-binary, gender fluid, and literally any human being. That’s because we all are born with a small amount of breast epithelial tissue—cells in the breast that can grow, develop, and eventually produce and deliver milk to nursing infants.

Weird quirk of biology, but that’s how it goes. We all have a little breast tissue (unless we get it removed), so we can all theoretically get breast cancer. In the figures below, you can see a schematic of how epithelial tissue appears at birth and how it grows in response to hormone signals during puberty, as well as how the network of epithelial tissue from a mouse actually looks under a microscope. For more on how the process works, see my previous post on breast anatomy, structure, and function.

**Note – mice and other mammals have mammary epithelial tissue to make milk, which is one of the defining characteristics of a mammal, and the growth and development of mouse mammary epithelium is very similar to that in humans.**

During puberty, biological female breast epithelial tissue grows in response to female hormones like estrogen and progesterone. For biological males, the epithelium doesn’t grow in response to male hormones like testosterone, leaving only a small cluster of epithelium behind. Since biological females grow more epithelium and are exposed to hormones that make these cells grow, they have a greater risk for developing breast cancer. But biological males are still at risk, since the small amount of breast epithelium left behind after puberty can become cancerous.

How does this happen? First of all, the number one risk factor for cancer in general is age. See my previous blog posts, Intro to Cancer and Cancer 101, for how normal cells become cancer. CNN version – it involves random mutations in DNA that alter genes that tell cells to grow and/or in a small percentage of cases inherited gene variants like BRCA1 and BRCA2 (see previous post on how BRCA genes work). If enough of these mutations accumulate over time in a breast epithelial cell, that cell can transform into cancer.

While more rare in biological males, get enough mutations in a breast epithelial cells and you get male breast cancer. About 1 in every 100 breast cancer cases diagnosed in the United States is found in a man. According to the CDC, risk factors include: getting older, genetic mutations and a family history of breast cancer, previous radiation therapy in the chest area, hormone therapy treatment for prostate cancer, Klinefelter syndrome (in which a person has an extra X chromosome), some conditions that affect the testicles (like injury or removal), liver disease, being overweight, and being obese.

If you have a family history of breast cancer and ovarian cancer, consider genetic counseling and testing for BRCA1 and BRCA2 variants associated with increased risk of breast cancer. In men, mutations in these genes can increase the risk for breast cancer, prostate cancer, and pancreatic cancer (see CDC).

As with female breast cancer, early detection and diagnosis is key for a good prognosis. Pay attention to your body and any changes in your breast area, and look for symptoms including:

A lump or swelling in the breast.
Redness or flaky skin in the breast.
Irritation or dimpling of breast skin.
Nipple discharge.
Pulling in of the nipple or pain in the nipple area.

Also, don’t let stigma, shame, or toxic masculinity keep you from seeking help and advice from your healthcare provider. Since male breast cancer is rare, you may feel like you’re alone, but there are resources and survivor networks available to help, ones that are decidedly not pink and are tailored for men. Ask your healthcare provider about local and online support groups, mental health support, and other resources. For more information on male breast cancer, check out these resources: Breastcancer.org, The National Cancer Institute, The American Cancer Society, The National Breast Cancer Foundation, Susan G. Komen.