Breast cancer is not just one, monolithic disease. It can present as a number of different types and stages, and these variations lead to differences in the way the individual disease is treated and the patient’s prognosis.

One of the rarer forms of breast cancer, Paget’s disease of the breast, is involved in about 1 to 4 percent of breast cancer cases in the United States, the National Cancer Institute reports. Named for the British doctor Sir James Paget who connected the disease’s primary symptoms to incidence of breast cancer in 1874, Paget’s disease involves the skin of the nipple and of the areola, the darker circle of skin around the nipple.

Dr. Nikita Shah, medical oncology team leader for the Breast Cancer Specialty Section and medical director of the Cancer Risk Evaluation Program at UF Health Cancer Center — Orlando Health, says that Paget’s disease of the breast “is considered a malignancy, but a noninvasive malignancy involving the nipple-areola complex.” This means that although it’s cancerous, Paget’s itself is confined to the nipple and areola area where it started. However, it is often a sign of another cancer in the breast.

[See: A Tour of Mammographic Screenings During Your Life.]

The most common sign of Paget’s disease is red, flaky skin on the nipple or the areola. “It really looks like eczema,” Shah says. Typically there’s no pain associated with the disease, although it’s possible that as the skin flaking gets worse, the site could bleed leading to some tenderness, Shah says. The NCI notes that other symptoms can include a flattening of the nipple and “discharge from the nipple that may be yellowish or bloody.”

As a noninvasive form of cancer, Paget’s is not considered an aggressive or fast-moving disease, but it is often associated with another cancer in the same breast. The Mayo Clinic website explains that “most women with Paget’s disease of the breast have underlying ductal breast cancer, either in situ — meaning in its original place — or, less commonly, invasive breast cancer.”

Breastcancer.org reports that 97 percent of patients with Paget’s disease of the breast also have an underlying or second breast cancer or a tumor elsewhere in the breast. According to the NCI, as many as 50 percent of patients with Paget’s have a tumor that can be felt during a clinical exam. Therefore, after the suspected Paget’s has been biopsied, which Shah says is the only way to diagnose it, the patient should also undergo “full imaging and full work-up to make sure there’s not another cancer lurking behind the Paget’s.”

The nipple biopsy your doctor will perform to diagnose Paget’s could take a number of forms, the NCI reports, including a surface biopsy, in which a glass slide or other tool is used to scrape cells from the surface of the skin. Other patients may have a shave biopsy, in which the doctor uses a razor-like tool to remove the top layer of skin. A punch biopsy uses a circular cutting tool to remove a disc-shaped sample of tissue. Or you may have a wedge biopsy in which the doctor uses a scalpel to remove a small wedge of tissue. No matter which type of biopsy is performed, the harvested tissue will be sent to the lab for testing to determine whether you have Paget’s.

Although men can get Paget’s disease of the breast, it’s more common in women and it tends to affect women over the age of 50. The NCI reports the average age at time of diagnosis is 57 years, “but the disease has been found in adolescents and in people in their late 80s.”

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Doctors aren’t exactly sure how or why Paget’s develops, although there are a couple of working theories. Breastcancer.org reports that “one possibility is that the cancer cells start growing inside the milk ducts within the breast and then make their way out to the nipple surface. This would appear to explain why so many people with Paget’s disease of the nipple have a second area of cancer within the breast.” A second theory suggests that the cells of the nipple become cancerous, just as cells in other parts of the body can sometimes become cancerous. “This theory would explain the small number of people who: (1) only have Paget’s disease in the nipple, or (2) have a second breast cancer that appears to be completely separate from the Paget’s disease.”

Paget’s is typically treated with surgery. The NCI reports that for patients who do not have a palpable tumor, the nipple and areola will be removed and the rest of the breast conserved. This approach is typically “followed by whole-breast radiation therapy” to ensure all cancerous cells left behind are killed. For patients with a palpable tumor, a mastectomy — a procedure in which the entire breast is removed — is often the preferred approach. These patients may also undergo a sentinel lymph node biopsy to determine whether the cancer has spread to nearby lymph nodes. If cancer is found in the lymph nodes, these patients may have additional surgery to remove other lymph nodes, and depending on the type and stage of the cancer that’s found in the removed tissue, some may be prescribed chemotherapy or hormone therapies.

The NCI reports the five-year survival rate for all women in the U.S. diagnosed with Paget’s disease between 1988 and 2001 was 82.6 percent. The prognosis is naturally worse for patients with later stage disease and better for those who find the disease earlier. The five-year survival rate for patients with both Paget’s disease of the breast and invasive cancer in the same breast is 95.8 percent if it’s caught at stage 1. Stage 2 patients have a 77.7 percent survival rate. That rate drops to 46.3 percent in stage 3 and 14.3 percent in stage 4.

[See: Breast Pain? Stop Worrying About Cancer.]

If you notice any redness or flaking of the skin of the nipple or areola, see your doctor as soon as possible. Although it could be just an area of dry skin — “not every patch of dry skin is Paget’s,” Shah says — it’s important to get it checked out to be sure. The NCI reports that because early symptoms of Paget’s often don’t seem alarming and may be mistaken for just a patch of dry skin, “it may be misdiagnosed at first.” This means that people with the disease may have “had symptoms for several months before being correctly diagnosed.” As with all types of breast cancer, the earlier Paget’s is detected, the better your prognosis will be.

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What Is Paget’s Disease of the Breast? originally appeared on usnews.com