High Grade Colorectal Adenocarcinomas with SMAD4 Deficiency.

Poor prognosis has been reported for patients with SMAD4 deficient (dSMAD4) colorectal adenocarcinomas (CRCs). However, it remains unclear whether unique tumor morphologies or other advanced disease signatures might stratify those patients. To reappraise this possibility across a homogenous cohort of CRC patients with advanced-stage disease, we leveraged next generation sequencing (NGS) data to identify fifty dSMAD4 CRCs at our institution. An equal number NGS-verified SMAD4 proficient (pSMAD4) CRCs were identified in parallel, yielding a control group with similar demographics, clinicopathologic parameters, and background genetic drivers as the dSMAD4 test group. Although both groups progressed to AJCC stage IV metastatic disease at high rates (dSMAD4: 90%, pSMAD4: 86%), dSMAD4 CRC specimens were enriched with overtly high-grade (HG) mucinous and non-mucinous histomorphologies (dSMAD4: 44%; pSMAD4: 12%; p=0.0007). The HG subset drove poor prognosis in dSMAD4 CRCs, as those patients developed widely metastatic disease (p=0.0048) with short overall and progression-free survival (p≤0.0001). Metastasis of unknown primary was not uncommon for HG dSMAD4 CRCs, posing diagnostic challenges in those instances. However, all dSMAD4 CRCs retained positive immunolabeling for either CDX2 or SATB2 irrespective of grade, thereby aiding diagnosis and distinguishing the HG subset from other HG CRCs that lose these biomarkers. Our reappraisal identifies an underappreciated class of HG dSMAD4 CRCs that progresses rapidly to widely metastatic disease with a dismal prognosis. Although HG morphologies may mask CRC origins, immunohistochemistry retains diagnostic utility for dSMAD4 CRCs.