This video presents a pathology case involving a 2 cm breast mass in a 60-year-old man, diagnosed as Mammary Type Myofibroblastoma (MTMB). The histological analysis highlights key diagnostic features, including a well-circumscribed subcutaneous mass composed of fascicles separated by strikingly thick, coarse bundles of "ropey" collagen and bland spindle cells that often exhibit a characteristic "zigzagging" arrangement. The discussion confirms that MTMB is part of the RB1 loss group of tumors, sharing significant overlap with spindle cell lipoma, but typically demonstrating more prominent collagen and frequent co-expression of CD34 and Desmond. Clinically, MTMB is benign, cured by simple excision, and is now known to occur equally in men and women, as well as in various extra-mammary sites.
Mammary Type Myofibroblastoma: A Classic Pathology Case Review
0:17 Case Introduction: Presentation of a 2 cm breast mass in a 60-year-old man.
0:26 Histological Features: The mass is described as a well-circumscribed, unencapsulated subcutaneous lesion composed of fascicles. The key diagnostic feature noted is the presence of very thick, coarse bundles of "ropey collagen" dividing these fascicles.
0:59 Cellular Morphology: The lesion contains bland spindle cells with very rare atypia, sometimes showing incomplete palisading.
1:28 Diagnosis: Mammary type myofibroblastoma (MTMB).
1:57 Molecular Grouping: MTMB is classified within the RB1 loss group of tumors, which also includes spindle cell lipoma (SCL). MTMB and SCL share overlapping features and may be closely related fibroblastic entities.
2:44 Differentiation from SCL: MTMB is characterized by much more prominent ropey collagen bundles and the spindle cells tend to arrange in dramatic clusters between the collagen, often creating a "zigzagging shape."
3:19 Immunoprofile: MTMB exhibits RB1 loss, is usually positive for CD34, and commonly expresses Desmond (Desmond positivity is a key feature distinguishing it from most SCLs).
3:46 Clinical Relevance: Although initially associated with the breast in older men, MTMB also occurs in women (often detected via screening) and can be found in extra-mammary sites (hence the name "mammary type" myofibroblastoma).
4:16 Key Takeaway (Prognosis): MTMB is a benign tumor and is typically cured by simple excision.
5:22 Differential Diagnosis: The tumor appearance (particularly due to dilated vessels which can sometimes be present) could potentially mimic a solitary fibrous tumor (SFT), but STAT6 testing would easily resolve this.