Potential Diagnostic Pitfalls in Evaluating Immunohistochemistry for Cervical Myofibroblastomas.

Cervicovaginal myofibroblastoma (CVM) is a rare benign mesenchymal tumor of the lower female genital tract that shows chromosomal loss of 13q14 (RB1 gene located in this region). The aim of this study was to investigate the utility of immunohistochemistry (IHC) for desmin, CD34, and Rb in diagnosing CVM. All cervical polyps diagnosed from July 2016 to July 2017 were retrospectively reviewed. Cases showing morphologic myofibroblastic differentiation were evaluated by IHC for desmin, CD34, and Rb. Desmin and CD34 staining was recorded as positive or negative. Rb nuclear staining was graded as follows: 0 (<10%), 1 (10%-25%), 2 (>25%-50%), 3 (>50%-75%), or 4 (>75%). Intact nuclear expression of Rb in endothelial cells served as an internal positive control. IHC was performed on 76 cases with 14 excluded from the final cohort due to poor Rb internal control. A total of 61/62 (98.4%) cases were positive for desmin and CD34 with the following Rb distribution: grade 0 (n=53, 86.9%), grade 1 (n=5, 8.2%), grade 2 (n=2, 3.3%), and grade 3 (n=1, 1.6%). One case negative for desmin and CD34 showed grade 3 Rb staining. Upon rereview of the histology, 7/175 cases (4%) were morphologically and immunohistochemically compatible with CVM (desmin and CD34+ grade 0 Rb staining). CVM is a rare and under-recognized entity (4% of cervical polyps) for which morphology remains the mainstay of diagnosis. IHC reliance serves as a potential diagnostic pitfall as 86.9% of cases showing myofibroblastic differentiation demonstrated the staining pattern of desmin and CD34 positivity and Rb deficiency.