Metaplastic breast cancer (MpBC) is a rare and aggressive form of breast cancer, making up less than 1% of all breast cancer diagnoses. This distinct type of cancer is characterized by its unusual cellular composition, which often makes it more challenging to treat compared to more common breast cancer types. MpBC is frequently classified as triple-negative, meaning it lacks the common receptors for estrogen, progesterone, and HER2 protein, which significantly limits targeted treatment options.
Understanding Metaplastic Breast Cancer
Metaplastic breast cancer is distinguished by its unique pathological characteristics, specifically the presence of two or more distinct cell types within the tumor. This mixed cellular makeup contributes to MpBC’s aggressive behavior and rapid growth.
A significant proportion of MpBC cases are identified as triple-negative breast cancer (TNBC), meaning they do not express estrogen receptors (ER), progesterone receptors (PR), or human epidermal growth factor receptor 2 (HER2). The absence of these receptors means that therapies targeting these specific pathways, such as hormone therapy or HER2-targeted drugs, are generally ineffective for MpBC, narrowing the available treatment choices. Most metaplastic breast cancers are also high-grade, indicating that the cancer cells look very abnormal and grow quickly in a disorganized manner.
Staging Metaplastic Breast Cancer
Cancer staging is a system used by medical professionals to determine the extent of the disease, which helps guide treatment decisions and predict outcomes. The most common system for breast cancer, including metaplastic breast cancer, is the TNM (Tumor, Node, Metastasis) system. This system evaluates three main aspects: the size and extent of the primary tumor (T), whether the cancer has spread to nearby lymph nodes (N), and whether it has spread to distant parts of the body (M).
Stage 3 breast cancer, also known as locally advanced breast cancer, means the cancer has grown beyond the immediate area of the breast and may involve nearby lymph nodes or chest wall, but has not spread to distant organs. While MpBC is often larger at diagnosis and tends to spread through the bloodstream rather than primarily through lymph nodes, the TNM criteria still apply to define its stage.
Survival Rates and Influencing Factors
Survival rates for metaplastic breast cancer are generally lower than those for more common breast cancer types, reflecting its aggressive nature and typically triple-negative status. For Stage 3 metaplastic breast cancer, the five-year progression-free survival rate has been reported as 27%. The five-year overall survival rate for Stage 3 MpBC is approximately 30%.
Several elements influence the prognosis and survival rates for individuals with MpBC. Tumor grade is a significant factor, with most MpBC cases being high-grade, meaning the cells are highly abnormal and grow rapidly. The patient’s age at diagnosis and their overall health status also play a role in determining prognosis. Response to initial treatment can also impact long-term outcomes, as can the specific cellular components within the tumor, although treatment approaches are generally similar across MpBC subtypes. The presence of distant metastasis, particularly to organs like the lungs or brain, is associated with significantly poorer survival.
Treatment Approaches for Metaplastic Breast Cancer
Treatment for Stage 3 metaplastic breast cancer typically involves a multidisciplinary approach, combining several modalities. Surgery is a primary treatment, often involving a mastectomy (removal of the entire breast) or lumpectomy (removal of the tumor with surrounding tissue) along with dissection of nearby lymph nodes. Mastectomy may be more frequently recommended due to the larger tumor size often seen in MpBC.
Chemotherapy is commonly used, and due to the frequent triple-negative nature of MpBC, aggressive regimens are often employed. However, MpBC tumors can show resistance to standard chemotherapy drugs, making effective systemic treatment a challenge. Radiation therapy is also a common component of treatment, particularly after breast-sparing surgery or in cases with larger tumors or extensive lymph node involvement. Targeted therapies are generally not effective for MpBC because these tumors typically lack estrogen, progesterone, and HER2 receptors, which are the targets for many such drugs. Ongoing research into novel treatments and participation in clinical trials are important considerations for this rare and challenging cancer type.