While most breast lumps are not cancerous or represent a cancer that started in the breast, it is possible for cancer from another part of the body to spread there. The appearance of a cancerous tumor in the breast that originated elsewhere is an uncommon occurrence. This situation presents different diagnostic and treatment challenges compared to more common forms of breast cancer.
Understanding Secondary Breast Cancer
Metastatic cancer is the process by which cancer cells break away from their original, or primary, tumor and travel to other parts of the body. These migrating cells can establish new tumors in distant organs or tissues. When this process results in a tumor in the breast, it is called secondary breast cancer, indicating the cancer did not begin in the breast tissue itself. This is different from primary breast cancer, which originates in the breast’s ducts or lobules.
The spread of cancer cells to a new location is a complex journey. Cells from the primary tumor must invade nearby tissue and then gain access to transport pathways like the bloodstream and the lymphatic system. Once in circulation, the cancer cells can travel to distant sites, like the breast, exit the vessels, and begin to grow into a new tumor.
Metastases to the breast are relatively rare, accounting for an estimated 0.5% to 2.0% of all breast malignancies. The presence of a secondary tumor in the breast usually signifies that the primary cancer is widespread. These secondary tumors are often found in the fatty tissue of the breast rather than the glandular tissue where primary breast cancers develop.
Primary Cancers That Spread to the Breast
A variety of cancers can metastasize to the breast, though some do so more frequently than others. The most common source of a metastatic breast lesion is a primary cancer in the opposite breast. When considering cancers from outside the breast, malignant melanoma is one of the most frequently reported primary tumors to spread to the breast.
Lung cancer is another significant source of breast metastases. Cancers of the blood and lymphatic system, such as lymphoma and leukemia, are also common culprits. These cancers are systemic by nature, meaning they circulate throughout the body, which can lead to their accumulation in the breast tissue.
Other primary cancers known to spread to the breast include those originating in the ovaries, stomach, and kidneys. Sarcomas, which are cancers of the connective tissues like bone and muscle, can also metastasize to the breast. In men, prostate cancer is a frequent primary site for breast metastases.
The Diagnostic Process
The diagnosis of secondary breast cancer often begins with the discovery of a lump. These tumors typically present as a single, firm, and painless mass that is noticeably mobile under the skin. Unlike primary breast cancers, secondary tumors do not usually cause skin or nipple retraction. The presence of multiple or bilateral tumors is more suggestive of metastatic disease than a new primary cancer.
Imaging tests like mammograms and ultrasounds are standard first steps. On a mammogram, metastatic tumors often appear as round, well-defined masses. They lack the spiculations, or spiky projections, and microcalcifications that are often associated with primary breast cancers. Ultrasound imaging may show a well-circumscribed mass with internal echoes and increased blood flow.
While imaging provides important clues, a biopsy is the only way to definitively diagnose secondary breast cancer. A pathologist, a doctor who specializes in examining tissue, analyzes a sample of the tumor under a microscope. The task is to determine if the cells’ characteristics match those of a primary breast cancer or if they resemble cells from a cancer elsewhere in the body, which confirms the tumor’s true origin.
Treatment Guided by the Original Cancer Source
The treatment for secondary breast cancer is fundamentally different from that for primary breast cancer. The therapeutic strategy is dictated entirely by the original cancer’s type and location. For instance, if melanoma has spread to the breast, it is treated with therapies designed to fight melanoma, such as immunotherapy, not with treatments typically used for primary breast cancer.
This distinction is because the cancer cells in the breast retain the characteristics of the primary tumor. Therefore, treatments like lumpectomy, mastectomy, or hormone therapies common for primary breast cancer are generally not the primary approach. The goal of treatment is to manage the cancer systemically, as its presence in the breast indicates it has spread throughout the body.
Treatment options may include chemotherapy, targeted therapies, or radiotherapy, depending on the specifics of the primary cancer. Palliative care, which focuses on relieving symptoms and improving quality of life, may also be a component of the treatment plan.