Colonic tubular adenoma with clear cell change - case report with whole exome sequencing and updated review of the literature

Introduction: Colorectal tubular adenomas displaying clear cell change are rare entities, with unknown clinical relevance, prognosis, immunohistochemical, and molecular features. Case presentation: Hereby we report a case of a 43-year-old female patient with a rectosigmoid polyp. Histologically, conventional dysplasia was visible with scattered areas displaying clear cell change. Whole exome sequencing (WES) was carried out and revealed high tumour mutation burden, and 7 pathogenic mutations, including TP53, APC, FGFR4, EHBP1, IL4R, TYR, and ACTN3. Conclusion: Clear cell change may only be present in less than 0,1% of adenomas. Aetiology is not well understood, additionally, few authors suggest autolysis or fixation problems. Our WES resulted in newly found pathogenic mutations, and high mutation burden, proving the lesion's neoplastic origin. Hitherto, neither special stainings, nor immunohistochemical markers proved to be useful in the diagnostic process. From a differential diagnostic perspective, enteroblastic differentiation, primary and secondary clear cell adenocarcinoma has to be excluded.