Four cases diagnosed with gastric SMARCA4-UTs were all male, aged between 61 and 82 years. These tumors presented with ulcerated and advanced tumors, staged as tumor-node-metastasis (TNM) IV in cases 1, 2 and 4, and TNM IIIA in case 3. Tumor size varied from 2 to 6 cm in maximum diameter. Detailed clinical features are summarized in Table 1.

A 61-year-old male patient (case 1) who presented with dysphagia, abdominal pain and bloating for approximately one month was admitted to our hospital. A computed tomography (CT) scan of the abdomen showed a 6 cm irregular thickened tumor in the cardia, fundus and lesser curvature of the stomach (Fig. 1A). There were multiple enlarged lymph nodes in the ligamenta hepatogastricum, portacaval space, mesentery and abdominal aorta, which were partially fused, and a nodule in right posterior lobe of the liver. Gastroscopy showed a large ulcerative tumor in the cardia of the stomach, and a biopsy was performed. The clinical TNM stage was TNM VI. The patient received neoadjuvant therapy with a combination of chemotherapy (irinotecan and cisplatin) and sintilimab (a PD-1 inhibitor). A partial response (PR) was achieved after two cycles. The patient received continued treatment after six cycles with progressive disease (PD). Subsequently, this patient received the second line chemotherapy with albumin paclitaxel combined with tigio, and a PR was achieved after three cycles in clinical assessment. And then, surgical resection was performed.

Radiological, histopathological and immunohistochemical characteristics of case 1. A CT scan of the abdomen showed a large irregular thickened area of the cardia, fundus and lesser curvature of the stomach before neoadjuvant therapy(A). The tumor showed a solid architecture with undifferentiated morphology before (B, magnification x200) and after neoadjuvant therapy (C, magnification x200). There was no obvious response to neoadjuvant therapy (TRG3) (C, magnification x200). However, the lymph nodes showed a response to neoadjuvant therapy (D, magnification x10). Both biopsy and surgical resection specimen showed similar immunohistochemical staining. BRG1 was deficient expression in the nucleus of tumor cells. Both PCK and EMA were negative expression. The Ki67 proliferation index was approximately 80%. SALL4 and Syn were positively stained. P53 was positively expressed. (Magnification x200)

A 64-year-old male patient (case 2) presented with intermittent hematemesis and abdominal pain for three months. The CT scan of the abdomen and gastroscopy showed a 2 cm thickened lesion in lower esophagus and cardia of the stomach (Fig. 2A-B). A biopsy was performed. Besides, the CT scan showed multiple nodules in liver, indicating metastases of the liver; Additionally, lymph nodes in hepatogastric ligaments and portal space were enlarged and partially fused. The clinical TNM stage was TNM VI.

Gastroscopic, radiological, histopathological and immunohistochemical characteristics of case 2. Gastroscopy (A, arrow) and CT scan (B, arrow) showed a thickened lesion in lower esophagus and cardia of the stomach. The tumor showed a solid architecture with undifferentiated morphology (C, magnification x40) with focal necrosis (D, arrow, magnification x200). Partial tumor cells showed a rhabdoid morphology (E, magnification x200). BRG1 was deficient expression. Immunohistochemical staining showed negativity for both PCK and EMA, diffuse positivity for SALL4, and partial positivity for Syn. P53 was positively expressed. The Ki67 proliferation index was approximately 90%. (Magnification x200)

A 61-year-old male patient (case 3) presented with upper abdominal discomfort with bloating for approximately one month and was admitted to the local hospital. Gastroscopy was performed and showed a 4 cm mass in the lateral posterior wall of the stomach. Gastrectomy was performed at the local hospital. The pathological TNM stage was T4aN1M0, IIIA. The patient received chemotherapy after surgical resection.

An 82-year-old male patient (case 4) presented with abdominal pain for approximately one month and was admitted to the local hospital. A CT scan of the abdomen showed a 3 cm thickened and transmural mass in the antrum of the stomach, and metastatic nodules in the adjacent omentum and peritoneum. Multiple lymph nodes in the abdominal cavity and retroperitoneum were enlarged and fused. Gastroscopy was performed at the local hospital and a biopsy was performed. The clinical TNM stage was TNM VI.

Cases 3 and 4 were admitted and treated at the local hospital, and pathological consultation was submitted to our hospital. All four cases had similar histological characteristics. Morphological observation showed undifferentiated tumor cells that formed a solid architecture without tubular glandular formation (Figs. 1B-C, 2C-E and 3A-B, and 4A-B). The large- to medium-sized tumor cells were epithelioid ovoid or polygonal cells with abundant cytoplasm. Round, pleomorphic nuclei with prominent nucleoli were large and irregular. Mitoses were frequent. Cases 2 and 3 showed focal necrosis (Figs. 2D and 3A) and focal rhabdoid morphology (Figs. 2E and 3C).

Histopathological and immunohistochemical characteristics of case 3. The tumor showed a solid architecture with comedonecrosis (A, arrow). High-power view showed undifferentiated tumor cells with poor cohesion (B, magnification x200). Partial tumor cells showed a rhabdoid morphology (C, magnification x400). BRG1 was deficient expression. PCK was negative expression. Expression of p53 was completely loss. CD34 and Syn were positively stained. The Ki67 proliferation index was approximately 80%. (Magnification x200)

Histopathological and immunohistochemical characteristics of case 4. A low-power view (A, magnification x40) and high-power (B, magnification x400) of the tumor showed a solid pattern with undifferentiated morphology. Immunohistochemical staining showed negative expression of CK7, deficient expression of BRG1 and positive expression of p53. This case showed mismatch repair deficiency (dMMR), with deficient expression of MLH1 and PMS2, and retained expression of MSH2 and MSH6 (Magnification x200)

The tumor regression grade (TRG) for case 1 with neoadjuvant therapy was TRG3 (without an obvious response to neoadjuvant treatment) (Fig. 1C), while the lymph nodes showed a response to neoadjuvant therapy (Fig. 1D).

All four specimens showed complete loss of SMARCA4 (BRG1) in the tumor nuclei, with endothelial and inflammatory cells as internal positive controls (Figs. 1, 2, 3 and 4), and showed negative expression of epithelial markers, including PCK, EMA and/or CK7. Immunohistochemical staining showed SMARCB1 (INI1) retained expression (3/3, cases 1, 2 and 3), partial positivity for Synaptophysin (Syn) (3/3, cases 1, 2 and 3) and positivity for spalt-like transcription factor 4 (SALL4) (2/2, cases 1 and 2) in available cases. Mutant p53 expression occurred in four cases, resulting in strong and diffuse staining in cases 1, 2 and 4, and complete loss of p53 expression in case 3. The Ki67 proliferative index exceeded 80%. 25% (1/4, case 4) of cases had mismatch repair deficiency (dMMR).

The tumor cells of case 1 showed negative staining for PCK, EMA and CK7, diffuse positivity for SALL4 and Syn (Fig. 1). The tumor cells were negative expression of CD34, chromogranin A (CgA), CD56, CK5/6, nuclear protein in testis (NUT), CDX2, CD117, CD20, CD5, CD3, CD79a, CD30, S100, LCA, HMB45, MUM1, CD43, MPO, TDT and p63. MLH1, MSH2, MSH6 and PMS2 were retained expression. The expression of p53 was strong and diffuse staining, and the Ki67 proliferative index was approximately 80%. The immunohistochemistry staining of the resected specimen was similar to that of the biopsy.

The tumor cells of case 2 was negative expression of PCK, EMA and CK7, diffuse positivity for SALL4 and partial positivity for Syn (Fig. 2). The tumor cells were negative expression of CgA, CD56, CK5/6, CK20, Myogenin, MyoD1, Desmin, CEA, S100, CK8/18, CDX2, CD20, CD5, CD3, CD79a, LCA and HMB45. MLH1, MSH2, MSH6 and PMS2 were retained expression. The expression of p53 was strong and diffuse staining, and the Ki67 proliferative index was approximately 90%.

The tumor cells of case 3 was diffusely positivity for CD34 and Syn (Fig. 3). The tumor cells were negative expression of epithelial markers, including PCK, EMA, CK8/18, CK20 and low molecular weight keratin (CAM5.2), as well as CgA, CD56, S100, HMB45, CD117, DOG1, CD99, WTI, Desmin and SMA. MLH1, MSH2, MSH6 and PMS2 were retained expression. The expression of p53 was complete loss, and the Ki67 proliferative index was approximately 80%.

The tumor cells of case 4 was negative expression of PCK, EMA and CK7. The present patient had mismatch repair deficiency (dMMR), with deficient expression of MLH1 and PMS2, and retained expression of MSH2 and MSH6 (Fig. 4). The expression of p53 was strong and diffuse staining, and the Ki67 proliferative index was approximately 80%.

In situ hybridization for EBER was negative in available cases (cases 1 and 2). The next-generation sequencing (NGS) of case 1 confirmed deletion mutations in SMARCA4, RAD51 and TSC2, and the tumor mutation burden (TMB) was 0.96 mutations/Mb. The NGS of case 3 confirmed that SV (structural variation) of SMARCA4 was caused by translocation of SMARCA4 and LDLR, and CDH4 was caused by translocation of CHD4 and NCAPD2; point mutation of KDR, AR, FBXW7, TP53, EP300 and APC; deletion mutation of FBXW7 and FANCA; The TMB was 5.3 mutations/Mb.