There are a number of specific metaplastic breast cancer characteristics. From the preponderance of triple negative tumors to the nodal involvement, many of these tumors display marked differences from the more common forms of breast cancer.
MpBC is defined primarily by the tumor composition. Most breast cancers cells arise from the glandular tissue but metaplastic breast cancer is made up entirely of other types of cells or mixed with glandular cells. Normal breast cells are called epithelial (glandular) cells but MpBC will also have mesenchymal cells which are bone, skin or muscle cells. This is the hallmark of MpBC.
Metaplastic breast cancer has a lower incident of nodal involvement than other types of breast cancer. Nodal involvement has been shown to be less common compared to typical breast adenocarcinomas, with an incidence ranging from 6 to 26%. MpBC tumors are larger at presentation and grow at a rapid rate.
MpBC tumors can be solely spindle cell or squamous cell or can contain an element of traditional Invasive Breast Cancer. Prognosis in these cases can be partially based on the grade and amount of Invasive Breast Cancer involve. Metaplastic breast cancer is suspected to be chemo resistant. That is to say not all MpBC tumors are chemo resistant but many are not responding as well to the third generation chemo drugs at the same rate as other triple negative cancers.
One metaplastic breast cancer characteristic is some tumors are claudin-low type of triple negative breast cancer, and some are basal-like, as the majority of triple negative cancers are.
Recurrence rates: Recurrence rates for node-negative MpBC have been reported to be between 35 and 62%. Disease free survival rates for metaplastic breast cancer are lower than traditional IDC.
Hormone receptor Status: Hormone receptor expression in metaplastic breast cancer is uncommon with reported estrogen/progesterone positivity in 0–17% of cases. Most, not all, MpBC tumors are triple negative.
Sonography Vs. Mammography: Many Metaplastic Breast Cancer tumors are missed on initial mammograms. Often sonography is a superior method for confirming the existence of an Metaplastic Breast Cancer tumor.
Rate of Occurrence: Often you will see the rate of occurrence for metaplastic breast cancer at below 1% although in some newer studies you will see it listed at below 5%.
Prognosis: Finding a prognosis for MpBC is quite difficult although almost all studies show that the overall survival rates when compared evenly with stage and grade of other Invasive Breast cancers is worse. However, almost every MpBC study done to date is retrospective or with very small cohorts, making a definitive prognosis difficult to pin down.