Thread by @Teclis82

1. #Breastpath Hey all, myofibroblastomas are really sweet. Let’s learn about them. @ADamronMD @TheKarenPinto @KRoSlideReview @Chucktowndoc @jennpincus @LizaMQuintana @drkennethtang @dr_MPrieto

2. Clinical: Uncommon tumors. Well circumscribed, may slowly enlarge over time. Size usu. up to 4cm. Historically (and on boards/RISE exams presently)more common in men, but now seem to occur equally in men and women.
See pubmed.ncbi.nlm.nih.gov/18976021/

3. A couple annotated low power pics.

4. Some medium power pictures. Note how striking the bright pink collagen is.

5. High power, annotated to include cytologic features.

6. IHC: Usually CD34+, smooth muscle markers+. Keratin negative. Also commonly express ER, PR.

7. Several variants. A couple to be aware of: infiltrative (may have histologic overlap with fibromatosis and, more ominously, fibromatosis like metaplastic ca). Keratins are important, especially on biopsy.

8. Epithelioid variant: Epithelioid instead of spindled cells, which may have a resemblance to inv lobular carcinoma. Read more about this variant here:

pubmed.ncbi.nlm.nih.gov/19390423/

9. Interestingly, they have a similar molecular alteration as spindle cell/ pleomorphic lipoma (deletion of long arm of chromosome 13, resulting in loss of Rb expression). Note some morphologic similarities between myofibroblastoma and spindle cell lipoma as well.

10. A couple other tumors with similar morphologic and molecular features:

Cellular angiofibroma (#gynpath): See nature.com/articles/modpa…

The recently described “atypical spindle cell lipomatous tumor” (#bstpath): See pubmed.ncbi.nlm.nih.gov/27879515/

11. Also note that myofibroblastomas are often found in other sites (outside of breast, they’re called ‘mammary-type myofibroblastoma). See pubmed.ncbi.nlm.nih.gov/26523539/

12. As an aside: “man with breast mass” on boards/RISE is usually myofibroblastoma or dude w/Klinefelters; in real life, it’s almost always gynecomasfia.

13. Prognosis: Benign. Thanks all