Metaplastic breast cancer is a rare, aggressive form of breast cancer. It is usually discovered as a fast-growing lump or mass in the breast.
In imaging exams, the tumor often looks like an invasive ductal carcinoma, a breast cancer that started in a milk duct and has spread to nearby tissue outside the duct. Metaplastic breast cancer tumors are usually larger at the time of diagnosis, though.
Under a microscope, metaplastic breast cancer cells look like a mix of different cancer types. This once led doctors to believe that it starts as two different cancers that joined at some point. However, emerging data suggest that metaplastic breast cancer is a single cancer that possibly began in very young cells with the ability to develop into different types of mature cells.
Metaplastic breast cancer prognosis
Compared to breast cancer overall, metaplastic breast cancer is faster growing and more likely to metastasize, or spread, to other parts of the body. It is also more likely to recur after a successful initial treatment.
The five-year survival rate of patients with metaplastic breast cancer is about 55%. This figure doesn’t include anyone diagnosed in the last few years who may have received new, more effective treatments, so the current survival rate may be higher.
Metaplastic breast cancer treatment
Metaplastic breast cancer makes up less than 1% of all breast cancer diagnoses. Because it is so rare, there have been few clinical trials dedicated to the disease. Based on current guidelines, it should be treated like other breast cancers at the same stage and with the same features.
Most metaplastic breast cancers have triple-negative receptor status. These breast cancers do not have high levels of the estrogen receptor, progesterone receptor, and HER2 gene/protein. Drugs that target these features of cancer cells do not work well against triple-negative cancers. Other treatment strategies are needed.
If a patient is diagnosed before the cancer has spread beyond the breast and surrounding lymph nodes, treatment usually starts with chemotherapy, possibly in combination with immunotherapy, to shrink the tumor. This treatment is followed by surgery and potentially radiation therapy.
If the cancer has spread beyond the breast and surrounding lymph nodes, it is usually treated with chemotherapy or other cancer drugs, either alone or in combination. Radiation may be used to reduce pain caused by a tumor mass.