Metaplastic carcinoma is an uncommon form of breast cancer, accounting for less than 1% of all diagnoses. The term “metaplastic” refers to a “change of form,” which describes this cancer’s core feature. It involves a transformation of cancer cells from a glandular appearance into other, non-glandular cell types. This change results in a tumor that often behaves more aggressively than common types of breast cancer.
Defining Characteristics of Metaplastic Carcinoma
Cancer cells that originate in the breast’s milk ducts undergo a “metaplasia,” changing into forms that resemble different tissues. When viewed under a microscope, pathologists can see a mixture of cell types within the same tumor.
This cellular differentiation leads to several subtypes, named for the cells the cancer mimics. The squamous cell subtype resembles skin cells, while the spindle cell subtype has elongated cells. Other forms include carcinosarcoma, which contains both epithelial and mesenchymal elements, and subtypes with bone or cartilage features. The specific subtype influences the tumor’s growth and behavior.
A defining molecular feature is the receptor status. The majority of these tumors are classified as triple-negative, meaning they lack receptors for estrogen, progesterone, and a protein called HER2. This is a distinction from many common breast cancers that are fueled by one or more of these factors.
Diagnosis and Staging
The diagnostic process often begins when a person discovers a palpable lump in the breast, which may have grown rapidly. A physician will order imaging tests like a mammogram or ultrasound to investigate the mass. An MRI may also be used to get a more detailed view of the tumor and surrounding tissue.
A definitive diagnosis requires a biopsy, which involves taking a small tissue sample from the suspicious area. A pathologist then examines this tissue under a microscope. The presence of mixed cell types confirms a diagnosis of metaplastic carcinoma.
Once cancer is confirmed, the next step is staging to determine the extent of the disease. Staging uses the TNM system: T for tumor size, N for cancer in nearby lymph nodes, and M for metastasis (spread to distant parts of the body). Metaplastic carcinomas are often larger and at a more advanced stage at diagnosis compared to other breast cancers.
Treatment Approaches
Surgery is the primary treatment for localized metaplastic carcinoma. The approach depends on the tumor’s size and may involve a lumpectomy (removing the tumor) or a mastectomy (removing the breast). During surgery, a sentinel lymph node biopsy is often performed to check if cancer has spread to the lymph nodes under the arm.
Following surgery, systemic therapies are recommended. Because most metaplastic carcinomas are triple-negative, chemotherapy is a main part of the treatment. Standard chemotherapy regimens, including drugs like anthracyclines and taxanes, are used to attack rapidly dividing cancer cells.
Since these tumors are triple-negative, treatments that target hormone receptors or the HER2 protein are ineffective. The cancer cells lack the receptors that therapies like tamoxifen or HER2-targeted drugs act upon. Radiation therapy is frequently used after surgery to reduce the chance of local recurrence. For advanced disease, newer treatments like immunotherapy are an active area of research.
Prognosis and Recurrence
The outlook for an individual with metaplastic carcinoma depends on several factors. The stage of the cancer at diagnosis is a primary element; cancers detected at an earlier stage, when the tumor is smaller and has not spread, have a more favorable prognosis. Other factors include the specific tumor subtype, its grade (how abnormal the cells look), and whether cancer is found in the lymph nodes.
Metaplastic carcinoma has a more aggressive course than common forms of breast cancer. These tumors have a higher tendency to grow quickly and to recur after initial treatment is completed. This higher tendency for recurrence underscores the importance of a comprehensive initial treatment plan.
Due to the risk of recurrence, long-term follow-up care is necessary. This involves regular check-ups and imaging tests to monitor for any signs that the cancer has returned, either locally or as distant metastases.