Correlation between KRAS and NRAS mutational status and clinicopathological features in 414 cases of metastatic colorectal cancer in Morocco: the largest North African case series.

BACKGROUND: Advances in molecular biology have improved understanding of the molecular features of carcinogenesis and progression of colorectal cancer. It is clear that the efficacy of anti-EGFR depends upon the RAS mutational status, since any mutation in RAS is associated with resistance to anti-EGFR therapy. The aim of this study is to report the largest North African description of KRAS and NRAS status in metastatic colorectal cancer and to describe the association of these mutations with clinicopathological characteristics. METHODS: This is a prospective study of all consecutive unselected metastatic colorectal cancer samples, collected from the Laboratory of Pathology at the National Institute of Oncology of Rabat, Morocco, from January 1st 2020 to December 31st 2021. The molecular analysis was performed on the Idylla™ platform (fully automated real-time polymerase chain reaction-based assay) for KRAS and NRAS mutations in exons 2, 3 and 4. These mutations were correlated to gender, primary tumor site, histological type and degree of differentiation of tumor using adequate statistical methods. RESULTS: Four hundred fourteen colorectal tumors were screened for KRAS and NRAS mutations. These mutations occurred in 51.7% of tumors for KRAS (mainly in exon 12) and in 3% of tumors for NRAS. There was a significant correlation between NRAS mutation and age of colorectal patients in this study. The low rate of invalid RAS tests (1.7% for KRAS and 3.1% for NRAS) was certainly obtained due to the strict respect of pre-analytical factors such as cold ischemia time and formalin fixation. CONCLUSION: We report the largest North African analysis of NRAS and KRAS status in colorectal metastatic patients. This study showed the ability in low middle income countries to perform a high rate of valid tests and the unusual trend towards older patients for NRAS mutations.

Diffuse malignant peritoneal mesothelioma mimicking ovarian cancer.

Diffuse malignant peritoneal mesothelioma (DMPM) and peritoneal carcinomatosis have similar computed tomography imaging features. Peritoneal carcinomatosis is a known metastatic site for many malignancies and particularly gastrointestinal tract and ovarian cancers. Also, DMPM can masquerade as an ovarian epithelial neoplasm, with very similar clinical presentation and an overlap in imaging findings. When no evident primary tumor is detected other than the peritoneal disease, primary malignant mesothelioma should be considered. Since accurate diagnosis is essential for treatment management, the gold standard in differentiating between these two entities lies in histological analysis. We report a case of DMPM that was initially misdiagnosed as an ovarian cancer, where the biopsy of a peritoneal nodule was able to correct and confirm the diagnosis of DMPM.