cow-2022-16

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1. Ebryonal Rhabdomyosarcoma.

The gross specimen showed a large(7.5 cm), well-circumscribed, solid gray-tan tumor compressing on the testis(Figure 1). On microscopy, the tumor was composed of spindled to poorly differentiated cells, embedded in a myxoid to fibrotic stroma; focal areas showed typical rhabdomyoblastic differentiation (Figures2, 3, 4). There were numerous mitotic and apoptotic figures with very limited areas of necrosis. The neoplasm involved the epididymis (Figure 5) and focally involved the periphery of the testis.

On immunohistochemistry, the tumor cells were strongly positive for myogenin(Figure 6) and very focally for desmin. AE1/AE3, smooth muscle actin (SMA), CD31, SOX10 and S100 were all negative. FISH testing for FOXO1 fusion gene was normal. The morphology and the immunoprofile support the diagnosis of embryonal rhabdomyosarcoma.

Rhabdomyosarcoma (RMS) is a malignant soft tissue neoplasm exhibiting embryonic skeletal muscle differentiation(1). Histological subtypes of RMS include embryonal, alveolar, pleomorphic and spindle cell/sclerosing; embryonal RMS is the most common subtype(1, 2).Common locations for embryonal RMS include the head and neck area and the genitourinary tract.(1).RMS is the most common soft tissue sarcoma of childhood and adolescence,but it is relatively rare in adults(3, 4). Paratesticular RMS accounts for approximately 7% of all RMS and embryonal RMS is the most common histologic subtype,followed by the alveolar and spindle cell subtypes (2, 3, 5).The affected age group ranges from 13 to 38 years with a median age of 16 years (5).The typical presentation of paratesticular RMS includes a rapidly enlarging painless scrotal mass(2, 3, 4). Serum tumor markers such as bHCG, AFP and LDH are usually not elevated(2).

Histologically, embryonal RMS is composed of primitive mesenchymal cells in various stages of myogenesis. They are embedded in a loose, myxoid stroma, comprised of alternating areas of dense and loose cellularity(1). Evidence of terminal differentiation,including cross-striation may also be seen(1). By immunohistochemistry, embryonal RMS variably expresses desmin, muscle-specific-actin (MSA), SMA, and also myogenin and MYOD1 that are considered more sensitive and specific(1).

The molecular profile of RMS differs by the histological subtype. Most cases of embryonal RMS exhibit loss of heterozygosity on the short arm of chromosome 11(1, 2).Alveolar RMS, which confers a worse prognosis, is characterized by PAX3-FOXO1 and PAX7-FOXO1 fusion genes(1). The lack of FOXO1 fusion gene in this patient signifies a potentially favorable prognosis.Up to a third of patients with RMS present with metastatic disease at the time of diagnosis(5).The tumor tends to spread via the lymphatics to the iliac and paraaortic lymph nodes, but hematogenous spread to the lung and liver can also occur(3, 4). Favorable prognostic factors include younger age at presentation, localized stage, smaller tumor size, adequacy of resection, and histological subtype,such as spindle cell and botryoid variants(2, 3, 4, 5, 6). Currently,there is no standardized management for paratesticular RMS,and the treatment usually includes a combination of surgery, chemotherapy,and radiation(2, 3, 4, 5).

1.  WHO Classification of Tumors, Soft Tissue and Bone Tumors. Available at: https://tumourclassification.iarc.who.int/home. Accessed Feb 27, 2022.

2. Zhu Y, Zhu Z, Xiao Y, Zhu Z. Case Report: Paratesticular Rhabdomyosarcoma. Front. Oncol. 11:629878. doi: 10.3389/fonc.2021.629878

3. Boudahna L, Benbrahim, Z, Amaadour L, Mazouz A, Benhayoune K, et al. Para testicular Rhabdomyosarcoma in Adults: three case reports and review of literature. Pan African Medical Journal. 2014; 19:279 doi:10.11604/pamj.2014.19.279.4784

4. Kumar R, Kapoor R, Khosla D, Kumar N, Ghoshal S, et al. Paratesticular Rhabdomyosarcoma in Young Adults: A tertiary Care Institute Experience. Indian J Urol. 2013 Apr-Jun; 29(2):110-113.

5. Keskin S, Ekenel M, Basaran M, Kilicaslan I, Tunc M, et al. Clinicopathological Characteristics and Treatment Outcomes of Adult Patients with Paratesticular Rhabdomyosarcoma (PRMS): A 10-year single-centre experience. Can Urol Assoc J. 2012 Feb; 6(1):42-45.

6. Newton WA, Gehan EA, Webber BL, Marsden HB, et al. Classification of Rhabdomyosarcomas and Related Sarcomas. Pathologic aspects and proposal for a new classification–an Intergroup Rhabdomyosarcoma Study. Cancer. 1995 Sept; 76:1073-85.

Crystal(Yitong)Xu; PGY-3, Anatomical Pathology, University of Calgary, Alberta, Canada
Email: yitong.xu@albertahealthservices.ca

Dr. Kiril Trpkov; Rockyview General Hospital, University of Calgary, Alberta, Canada
Email: kiril.trpkov@albertaprecisionlabs.ca

Testis

Embryonal rhabdomyosarcoma; paratesticular tumor; adult