A breast cancer diagnosis often marks the beginning of a long survivorship journey. As treatments improve and survival rates rise, the focus shifts to the risk of developing entirely new, unrelated cancers years later. Understanding these potential long-term risks is a major aspect of post-treatment care for survivors. A new cancer is different from metastasis, which occurs when the original breast cancer cells spread to distant parts of the body.
Distinguishing Secondary Cancer from Recurrence
The distinction between a secondary primary cancer and a recurrence is fundamental to understanding long-term survivorship risks. A breast cancer recurrence represents the return of the original disease, either locally, regionally, or distantly. This is a continuation of the initial cancer, stemming from the same original malignant cells.
In contrast, a secondary primary cancer (SPC), often referred to as a second malignancy, is a completely new disease. This new cancer originates from a different cell line in a different organ or in the opposite breast. For example, a survivor may later develop lung cancer, which is genetically and biologically separate from their previous breast tumor. The risk of developing an SPC is influenced by shared risk factors, such as genetics, and the long-term effects of the initial cancer treatment.
Specific Secondary Cancers and Highest Risk Types
The most common secondary primary cancer diagnosed after breast cancer treatment is a new cancer in the opposite, or contralateral, breast. Survivors have a significantly higher risk of developing a second primary breast cancer compared to the general population. This risk is particularly elevated for those who carry inherited genetic mutations, such as in the BRCA1 or BRCA2 genes, which increase susceptibility to multiple cancer types.
Beyond the breast, the risk for certain non-breast cancers is elevated in survivors. Endometrial cancer, which affects the lining of the uterus, is a concern, partly due to the use of specific hormone therapies. Survivors have an approximately 87% greater risk of developing endometrial cancer than the general population.
Ovarian cancer risk is increased, especially in women with BRCA mutations, which predispose them to both breast and ovarian cancers. Lung cancer risk is also elevated, particularly in patients who received chest wall radiation. Survivors may also have an increased risk for certain gastrointestinal cancers, such as colorectal cancer.
Understanding Treatment-Related Risk Factors
The therapies used to cure the initial breast cancer can sometimes contribute to the later development of a secondary primary cancer. One recognized treatment-related risk comes from radiation therapy, which targets and destroys cancer cells. However, the ionizing radiation can also damage healthy cells near the treatment field, increasing the risk for certain solid tumors.
Radiation to the chest wall, a standard part of breast-conserving therapy, is associated with an elevated risk of lung cancer in the irradiated field; this risk is much higher for survivors who smoke. Radiation has also been linked to a small risk of developing soft tissue sarcomas and bone cancers within the treated area. These secondary cancers often take many years to appear.
Certain chemotherapy drugs, particularly those known as alkylating agents, are associated with a greater risk of developing treatment-related leukemias. The most common forms are acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). The risk for leukemia increases with higher doses or longer duration of chemotherapy treatment.
The hormonal therapy Tamoxifen is highly effective in preventing breast cancer recurrence. However, it carries a small, known risk of increasing the chance of uterine cancer, specifically endometrial cancer and uterine sarcoma. While this side effect is a concern, the substantial benefits of Tamoxifen generally outweigh the low absolute risk of a secondary uterine malignancy.
Surveillance and Screening Post-Treatment
Managing the risk of a secondary primary cancer involves a commitment to consistent, personalized surveillance and screening protocols. For survivors who still have breast tissue, annual screening mammography is the standard of care to monitor for a new primary cancer in the remaining breast. Patients considered high-risk, such as those with dense breasts or a BRCA mutation, may also be advised to undergo a yearly breast Magnetic Resonance Imaging (MRI) in addition to their mammogram.
Screening for non-breast secondary cancers generally follows the same guidelines as those for the average-risk population, but certain past treatments or genetic factors require enhanced monitoring. For survivors who have taken Tamoxifen, it is important to be vigilant for any unusual vaginal bleeding, discharge, or spotting, as these symptoms can be an early sign of uterine cancer. Any such change should be reported immediately to a healthcare provider for follow-up testing.
Survivors should adhere to general population screening guidelines for other cancers, such as colonoscopy for colorectal cancer and regular gynecological check-ups. The surveillance plan should be individualized, taking into account the patient’s specific treatment history, age at diagnosis, and genetic risk factors.