Elusive and Aggressive: Unraveling SMARCB1/INI1-Deficient Undifferentiated Carcinoma With Rhabdoid Features Arising From the Colon: A Case Report and Comprehensive Literature Review

Abstract

Undifferentiated carcinomas are highly aggressive tumors with a dismal prognosis. A subset of these tumors has been associated with inactivation or mutations of the Switch/Sucrose Nonfermenting (SWI/SNF) remodeling complex. Our understanding of the relationship between the clinicopathological features and molecular profiling of SWI/SNF-deficient undifferentiated carcinoma is still evolving due to its rarity. We herein present a rare tumor of undifferentiated carcinoma with SMARCB1/INI1 deficiency arising from the colon. The histology revealed a tumor composed of sheets of discohesive, high-grade epithelioid cells with rhabdoid morphology along with anaplastic giant cells. Additionally, there was a significant infiltration of inflammatory cells in the background. Immunohistochemical (IHC) analysis supported the diagnosis of carcinoma with loss of INI1 expression, the tumor was mismatch repair protein proficient. Molecular analysis demonstrated an oncogenic KRAS mutation (p.G12D), whereas it was wild-type BRAF, and wild-type NRAS. The diagnosis of SWI/SNF-deficient undifferentiated carcinoma can be challenging. Correlation with clinical findings, in conjunction with IHC work-up and molecular analysis, is of utmost importance to arrive at the appropriate diagnosis and exclude potential mimics.

Keywords: INI1; SMARCB1; SWI/SNF; colon; undifferentiated carcinoma.

Figure 1.

(A) Poorly cohesive growth pattern was seen with medium-large rhabdoid tumor cells and a prominent inflammatory cell infiltrate (×200); (B) The tumor cells were positive for keratin AE1/AE3 (×400); (C) The tumor cells demonstrated loss of INI1 expression (note the positive internal control within the surrounding inflammatory cells) (×400). (D) The tumor cells showed diffuse cell membrane staining with claudin 4 (×200).

Figure 2.

Kaplan-Meier analysis demonstrated that SMARCB1/INI1 loss (A) and BRAF mutation (B) were significantly associated with poor overall survival in patients with rhabdoid undifferentiated colonic carcinoma.