Diagnosis

Diagnosis

Metastatic extrarenal rhabdoid tumor.

Discussion

Rhabdoid tumor is a rare malignant neoplasm of uncertain histogenesis that is composed of cells with rhabdoid (resembling rhabdomyoblasts) cytomorphology and characterized by biallelic mutations in the SMARCB1/INI1 tumor suppressor gene. Rhabdoid tumor occurs most commonly in infancy and early childhood and may arise in the kidney (renal rhabdoid tumor), brain (atypical teratoid-rhabdoid tumor), and other tissues (extrarenal rhabdoid tumor, ERT). ERT arises in a range of primary sites including soft tissue, the gastrointestinal, and genitourinary tracts. 

ERT can be sporadic or can occur as part of the rhabdoid tumor predisposition syndrome (RTPS). Children with RTPS have a higher incidence of multiple primary rhabdoid tumors and are often diagnosed at a younger age than patients with sporadic tumors. As exemplified in the index case, advanced-stage disease (stages III and IV) at presentation is common, occurring in about 70% of patients with ERT. The clinical presentation varies with the site of involvement. Soft tissue or visceral involvement may cause palpable masses and local pain. Seeding of serous membranes results in malignant effusions.

Grossly, ERT appears as a poorly circumscribed pale to-tan mass with frequent areas of hemorrhage and necrosis. On microscopy, the malignant cells are arranged in sheets, poorly cohesive groups, and infiltrating single cells. The tumor cells show a rhabdoid morphology with eosinophilic intracytoplasmic globules, vesicular nuclei, and prominent nucleoli. Mitoses and tumor necrosis are common. Areas of mucoid degeneration are frequent.

Although not epithelial in origin, the tumor cells mark with low molecular weight cytokeratins, EMA, and vimentin due to intermediate filaments contained in the intracytoplasmic inclusions. Other differentiation markers like S100 protein and Sox10 (neural crest); myogenin, desmin, and SMA (muscle); CD45 (lymphoid); CDX2 (gastrointestinal); NKX3.1 (prostate); TTF1 (lung), etc., are negative (figures 7-8). Loss of nuclear INI expression by immunohistochemistry reflects the presence of SMARCB1/INI gene alterations.

Treatment of ERT includes chemotherapy or radiation followed by resection. As in our patient, local recurrence and metastasis are common, and despite treatment, ERT remains a highly lethal tumor with a dismal 3-year survival rate of less than 20%.

References

1. Brennan B, Stiller C, Bourdeaut F. Extracranial rhabdoid tumours: what we have learned so far and future directions. Lancet Oncol. 2013;14(8):e329-e336. doi:10.1016/S1470-2045(13)70088-3

2. Geller JI, Roth JJ, Biegel JA. Biology and Treatment of Rhabdoid Tumor. Crit Rev Oncog. 2015;20(3-4):199-216. doi:10.1615/critrevoncog.2015013566

3. Luca AC, Miron IC, Cojocaru E, et al. Cardiac Rhabdoid Tumor-A Rare Foe-Case Report and Literature Review. Children (Basel). 2022;9(7):942. Published 2022 Jun 23. doi:10.3390/children9070942

4. Petitt M, Doeden K, Harris A, Bocklage T. Cutaneous extrarenal rhabdoid tumor with myogenic differentiation. J Cutan Pathol. 2005;32(10):690-695. doi:10.1111/j.0303-6987.2005.00383.x

5. Wu X, Dagar V, Algar E, et al. Rhabdoid tumour: a malignancy of early childhood with variable primary site, histology and clinical behaviour. Pathology. 2008;40(7):664-670. doi:10.1080/00313020802436451
    

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