Protruding structures with high expression of LGR5 are formed during regrowth phase after chemo-treatment in xenograft model of colorectal adenocarcinoma

Recurrence after chemotherapy is one of the biggest obstacles in cancer therapy, along with metastasis. Although histopathological evaluation in preclinical models like the xenograft model help us to understand the pathophysiological process of tumor growth, there are not enough detailed histopathological analyses of such models. In this study, to learn how a tumor recovers the typical tumor structure after structural corruption during chemo-treatment, xenografted tumors originating from a patient-derived xenograft of colorectal cancer (CRC) were analyzed histopathologically over time. There were many Duct (Flattened) at Day 1 (one day after the final administration of Irinotecan), but the ratio of Duct (Columnar) and Cribriform-structures typically found in colorectal adenocarcinoma-increased over time. Finally, at Day 15 (15 days after the final administration of Irinotecan), tumor structure and size were once again the same as in the control group. LGR5, a known cancer stem cell (CSC) marker for CRC, was highly expressed on protruding structures observed from Duct (Flattened) during their transformation into Duct (Columnar) and Cribriform. In addition, these LGR5-expressing protruding structures were either Ki67 negative or positive. These results suggest that the formation of protruding structures on Duct (Flattened) is a pivotal first step in the regrowth of tumors.