May 2023 – Cytopathology

Embryonal rhabdomyosarcoma.

This case was signed out on the surgical specimen as embryonal rhabdomyosarcoma involving left ovary, fallopian tube, and para-adnexal soft tissue. 

Rhabdomyosarcoma (RMS) is the most common soft-tissue malignancy of childhood and adolescence, however, adult RMS is rare, representing only 3% of soft tissue tumors and less than 1% of all adult malignancies. Primary abdominopelvic RMS is exceedingly uncommon, with only a few cases reported in the literature involving the fallopian tube and ovary as primary locations. The largest reported series of primary ovarian RMS is by Nielsen et al in 1998, and it included 13 cases in patients with age varying from 7 to 79 years. 

Histomorphologically, RMS exhibit patternless sheets of spindled, stellate, and ovoid cells with variable skeletal muscle differentiation. Typically, the embryonal subtype (ERMS) has primitive small cells with scant cytoplasm and abundant apoptoses. Rhabdomyoblasts with abundant eosinophilic cytoplasm (when elongated, called strap cells) with or without cross striations and multinucleated giant cells can also be seen. Mitotic activity is variable but often brisk. ERMS characteristically stain positive for desmin, myogenin, and myoD1 (typically coexpression of desmin and myogenin), assisting with differential diagnosis with other small round cell tumors. Rarely, the tumor cells can stain positive with CD99, cytokeratin, EMA, S100, ER, PR, or WT1. High Ki-67 expression is observed, especially in hypercellular areas. 

Metastatic sarcomas, including RMS, are rarely diagnosed in body fluids. Sarcoma cells in fluids can round up and lose the characteristic appearance seen on tissue biopsy, posing diagnostic challenges. Several studies have looked into the shared cytomorphologic features of sarcomas in body fluids, which can include single or small clusters of cells, large tumor cells, and occasional multinucleated giant cells. Prominent nucleoli and the chromatin patterns vary from case to case. Cytoplasm tends to be scant in nature and features of mesenchymal differentiation can be seen in some specimens. Mitoses are usually absent, even when easily identifiable on corresponding histologic sections. Knowledge of prior history and high level of suspicion are helpful in achieving the correct diagnosis.

Several genetic alterations have been associated with RMSs, one of which is DICER1 mutations (germline or somatic) that have been shown to be associated with ERMS cases of the cervix and genitourinary tract. DICER1 syndrome is a hereditary cancer predisposition syndrome that can result in a variety of “hyperplastic” disorders and uncommon neoplasms including various benign and malignant thyroid neoplasms, pleuropulmonary blastoma, ovarian Sertoli-Leydig cell tumor (SLCT), and ERMS of the cervix and genitourinary tract. 

The presence of primitive-appearing glands containing cytoplasmic vacuoles, which stain positive for SALL4 immunostain, and presence of cartilage foci that might be cytologically atypical, an uncommon finding in ERMS of other sites, should alert the pathologist for the possibility of an associated DICER1 mutation.

References

1. McCluggage WG, Apellaniz-Ruiz M, Chong AL, et al. Embryonal rhabdomyosarcoma of the ovary and fallopian tube: rare neoplasms associated with germline and somatic DICER1 mutations. Am J Surg Pathol. 2020;44(6):738-747. doi:10.1097/PAS.0000000000001442
2. Karram S, Geddes S, Li QK. Cytological diagnosis of metastatic sarcomas in body fluids and correlation with immunohistochemical/molecular studies: a retrospective study of cytologic cases. Am J Clin Pathol. Volume 144, Issue suppl_2, 1 October 2015, Page A091, https://doi.org/10.1093/ajcp/144.suppl2.091 
3. Abadi MA, Zakowski MF. Cytologic features of sarcomas in fluids. Cancer. 1998;84(2):71-76. doi:10.1002/(sici)1097-0142(19980425)84:2<71::aid-cncr1>3.0.co;2-g
4. Chen AL, Janko E, Pitman MB, Chebib I. Clinical, cytologic, and immunohistochemical features of sarcomas involving body cavity fluids. Cancer Cytopathol. 2019;127(12):778-784. doi:10.1002/cncy.22197
5. Gupta S, Sodhani P, Jain S. Cytomorphological profile of neoplastic effusions: an audit of 10 years with emphasis on uncommonly encountered malignancies. J Cancer Res Ther. 2012;8(4):602-609. doi:10.4103/0973-1482.106574