P-327 Comparison of clinicopathological and molecular features of two rare entities: Appendiceal carcinoma and small bowel adenocarcinoma

Appendiceal Carcinoma (AC) and Small Bowel Adenocarcinoma (SBA) are rare malignancies, accounting for approximately 5% of all gastrointestinal cancers. Due to its rarity, high-quality data must still be provided to guide treatment. We aimed to describe characteristics and outcomes of patients (pts) with AC and SBA. A retrospective analysis was performed of all patients diagnosed with AC and SBA at our institution from 2012 to 2022 and evaluated in the medical Oncology department. Clinical data were collected from a review of the medical record. Overall response rates (ORR), progression-free survival (PFS), and overall survival (OS) were assessed across treatment lines. Overall 33 pts were identified, 17 cases with AC and 16 with SBA. Median age was 66 years with 61% female. The first symptom at diagnosis was abdominal pain in 85% of pts, and 42% initially presented with stage IV disease. SBA primary location was in the duodenum, jejunum and ileum in 44%, 31%, and 25%, respectively. AC’s histological subtypes were globet cell/ex-goblet cell 70.6% and adenocarcinoma 29.4%, while SBA were 100% adenocarcinomas (21.4% MSI). 19 patients had a molecular profile made; mutation on the MAPK pathway was present in 67% (7 KRAS and 1 NRAS mut) of SBA vs 42% of AC (all KRAS mut). No statistically significant differences in age, sex, symptoms and tumor differentiation was identified between AC and SBA. However, stage IV was more frequent in SBA than AC (62.5% vs 23%; p=0.02). Twenty-nine pts (88%) underwent surgical resection for their primary tumor, with 62% receiving chemotherapy (ChT) in the adjuvant setting; FOLFOX was the most common adjuvant ChT. Appendectomy followed by right hemicolectomy (56%), and segmental bowel resection (81%) were the most frequent types of surgery for AC and SBA. The liver was the most common metastatic site for SBA, and the peritoneum for the AC. FOLFOX was the most common first-line ChT, and FOLFIRI was the preferred second-line therapy, plus antiangiogenic in 22%. Only 12% of pts started a 3rd line of treatment. The median OS from diagnosis was 61.8 months [95%CI 46-77 months) for the whole cohort, mOS was 80 vs 31 months for AC vs SBA (p=0.002), respectively. AC and SBA are uncommon gastrointestinal neoplasms. Stage IV extension at diagnosis and KRAS mutations were more common in SBA, with a poorer prognosis. Adjuvant and metastatic treatment options are extrapolated from colorectal carcinoma. Specific studies are needed for this population of pts.