Primary Papillary Colonic Adenocarcinoma With PDGFRA Mutation. A New Morphological Subtype? A Case Report and Review of Literature

Classic colon carcinomas are defined as adenocarcinomas, characterized by groups of medium/large cells with basophilic and polymorphous nuclei and an eosinophilic elongated cytoplasm, that rearrange on glandular structures. Signs of poor prognosis include high tumor budding, lymphovascular and perineural invasion, poor differentiation, positive margins, and CDX2 loss. Less frequent colon carcinoma subtypes are: mucinous, medullary, signet-ring cell, squamous cell, small cell and undifferentiated carcinoma, among others. In the following case report, we present a 65-year-old woman with a T2N0Mx colon carcinoma with a remarkable papillary and follicular histological appearance. The immunohistochemical stains confirmed an intestinal origin (CDX2+) and excluded a thyroid, gynecological, and urological metastasis, with tumor cells negative for GATA3, PAX8, TTF-1, and thyroglobulin. There was no loss of mismatch repair proteins and p53 showed a wild-type staining. next generation sequencing showed a platelet-derivated growth factor receptor alpha (PDGFRA) mutation. To the best of our knowledge, there have been only two examples of primary papillary colon carcinoma reported in the literature, and neither of them with a PDGFRA mutation. We describe one tumor and discuss its pathological features.