[Advances in tumor regression patterns and safe distance of distal resection margin after neoadjuvant therapy for...

Neoadjuvant therapy has been widely applied in the treatment of rectal cancer, which can shrink tumor size, lower tumor staging and improve the prognosis. It has been the standard preoperative treatment for patients with locally advanced rectal cancer. The efficacy of neoadjuvant therapy for rectal cancer patients varies between individuals, and the results of tumor regression are obviously different. Some patients with good tumor regression even achieve pathological complete response (pCR). Tumor regression is of great significance for the selection of surgical regimes and the determination of distal resection margin. However, few studies focus on tumor regression patterns. Controversies on the safe distance of distal resection margin after neoadjuvant treatment still exist. Therefore, based on the current research progress, this review summarized the main tumor regression patterns after neoadjuvant therapy for rectal cancer, and classified them into three types: tumor shrinkage, tumor fragmentation, and mucin pool formation. And macroscopic regression and microscopic regression of tumors were compared to describe the phenomenon of non-synchronous regression. Then, the safety of non-surgical treatment for patients with clinical complete response (cCR) was analyzed to elaborate the necessity of surgical treatment. Finally, the review studied the safe surgical resection range to explore the safe distance of distal resection margin.