Fallopian tube precursor lesions of serous ovarian carcinoma require L1CAM for dissemination and metastasis

Most high grade serous ovarian carcinomas (HGSC) arise from Serous Tubal Intraepithelial Carcinoma (STIC) lesions in the distal end of the fallopian tube (FT). FT secretory cells become malignant by accumulating genomic aberrations over 6 to 7 years before seeding of the ovarian surface, with rapid tumor dissemination to other abdominal structures thereafter. It remains unclear how nascent malignant cells leave the FT to colonize the ovary. This report provides evidence that the L1 cell adhesion molecule (L1CAM) contributes to the ability of transformed FT secretory cells (FTSEC) to detach from the tube, survive under anchorage-independent conditions, and seed the ovarian surface. L1CAM was highly expressed on the apical surface of STIC lesions and contributed to ovarian colonization by upregulating integrin and fibronectin in malignant cells and activating the AKT and ERK pathways. These changes increased cell survival under ultralow attachment conditions that mimic transit from the FT to the ovary. To study metastasis to the ovary, we developed a tumor ovary coculture model. We showed that L1CAM expression was important for FT cells to invade the ovary as a cohesive group. Our results indicate that in the early stages of HGSC development, transformed FTSECs disseminate from the FT to the ovary in L1CAM dependent manner.