Primary SMARCB1-deficient intestinal carcinoma: Clinicopathological and molecular characterization of three cases with analysis of published data.

SMARCB1-deficient carcinomas exhibit a broad anatomical distribution. Herein, we characterize primary SMARCB1-deficient intestinal carcinoma (SdIC), encompassing both colorectal and small bowel origins. As an exceptionally rare and aggressive entity, SdIC presents significant diagnostic challenges due to its propensity to mimic other malignancies and the paucity of comprehensive clinical data, thereby hindering early recognition and effective management. We retrospectively analyzed three cases of primary SdIC from our center and combined them with 11 previously reported cases characterized by confirmed loss of SMARCB1 expression via immunohistochemistry (IHC), identified through a systematic literature search. All 14 cases were evaluated for clinicopathological features, immunophenotypes, molecular profiles, treatment modalities, and prognostic factors. Most patients (median age, 62.5 years; predominantly male) presented with advanced-stage disease (Stage III or IV, 12/14). Tumors with confirmed SMARCB1 deficiency exhibited rhabdoid morphology. Immunohistochemically, these tumors demonstrated retained SMARCA4 expression but frequent loss of intestinal differentiation markers, including CK20 (2/9) and CDX2 (2/10). Molecular testing was performed in 13 of 14 patients, revealing alterations in SMARCB1 (4/6), BRAF V600E (6/9), RAS (4/8), and TP53 (5/6), along with a high tumor mutational burden (TMB-H, 4/6). Microsatellite instability-high (MSI-H) was observed in 2 of 10 tested patients. The median follow-up period was four months. Preliminary log-rank tests suggested that distant metastasis and a tumor size > 7.4 cm were associated with poorer survival (p < 0.05). Primary SdIC is a clinically and molecularly distinct subtype of intestinal carcinoma with aggressive behavior and poor prognosis. Our findings highlight the critical value of routine SMARCB1 testing and comprehensive molecular profiling for the early and accurate diagnosis of this disease. High-risk patients should be prioritized for inclusion in clinical trials. Greater awareness of this aggressive subtype can improve diagnosis and access to personalized therapeutic strategies.