Chemotherapy affects normal, healthy cells as well as breast cancer cells. This is why chemotherapy can cause hair loss, anemia, and diarrhea. In rare cases, exposing normal cells to cancer treatments such as chemotherapy and radiation therapy can cause a new, different type of cancer to develop many years after treatment.
A large study found that women who received chemotherapy for breast cancer were more likely to develop a specific type of leukemia called acute myeloid leukemia (AML) within 10 years of treatment than women who didn't get chemo for breast cancer.
It's VERY IMPORTANT to know that while the risk for AML was higher for women who got chemotherapy, the risk of AML is still very small. Women who got chemotherapy for breast cancer had a 1.8% risk of developing AML within 10 years of treatment. Women who didn't get chemotherapy had a 1.2% risk.
If you've had cancer treatment, it's very important that you regularly see a doctor who is familiar with your medical history and understands your special risks, and also gives you counseling, monitoring, and screening for possible complications from earlier treatment.