Cutaneous Metastasis of Rectal Cancer as a Diagnostic Challenge: A Clinical Case and Literature Review.

Background/Objectives: Metastatic colorectal cancer remains a fatal disease, with a 5-year survival rate lower than 15%. The most common metastatic sites are the lungs and the liver, while skin metastases are very rare and often indicate a poor prognosis with a lower survival rate. Methods. Herein, we present the clinical case of a 62-year-old female patient with rectal cancer metastases to the skin of the anogenital and abdominal regions, diagnosed 2 years after completion of treatment of the underlying disease. Results: Histological examination of the skin lesions revealed adenocarcinoma, and expression of the same immunohistochemical markers was also found in the primary tumor and in the cutaneous metastases. However, next-generation sequencing demonstrated differences in the mutational profiles of the primary tumor and metastasis to the skin. Somatic mutations in the APC, TP53, and PTPN11 genes were revealed in primary rectal adenocarcinoma, but another pathogenic TP53 mutation and a frameshift variant in the DYNC1I1 gene were found in cutaneous metastases. The patient underwent several courses of FOLFOX6 chemotherapy in combination with bevacizumab, but the treatment was unsuccessful. An analysis of 50 clinical cases from the literature concerning various manifestations of cutaneous metastases of rectal cancer showed a median survival of 8.5 months from the time of detection of the skin lesions. Conclusions: In this regard, careful skin examination of patients with rectal cancer and timely detection of cutaneous metastases are essential steps in the follow-up of patients who have undergone treatment of the primary tumor.