Distribution of residual cancer cells in bowel wall and its associated factors in patients with rectal cancer after preoperative VMAT with concurrent chemotherapy

Objective: To investigate the distribution of residual cancer cells (RCCs) in the bowel wall and its associated factors among patients with rectal cancer after preoperative volumetric modulated arc therapy (VMAT) with concurrent chemotherapy. Methods: A retrospective analysis was performed on the clinical data of 178 patients with locally advanced rectal cancer who received VMAT with concurrent chemotherapy followed by surgery in our hospital from April 2011 to April 2013. There were 124 males and 54 females, and the age range was from 23 to 84 years. T₁, T₂, T₃, and T₄ rectal cancer was found in 1, 2, 73, and 102 patients, respectively. All the RCCs in surgical specimens from different layers of the bowel wall were evaluated pathologically. Between-group differences were evaluated by Fisher's exact test, and the associations of preoperative T and N stages with postoperative ypT and distribution of RCCs in the bowel wall were determined by Spearman rank correlation test. Results: The rates of RCCs in the mucosa, submucosa, muscularis propria, and subserosa/perirectal fat surgical specimens were 15.2%, 27.0%, 46.6%, and 46.1%, respectively, for all patients, and were 20.0%, 36.7%, 69.2%, and 68.3%, respectively, for 120 patients with ypT₂₄ disease. Of all patients surgically treated, 52 had ypT₀ disease, 2 had ypT_is disease, 4 had ypT₁ disease, 38 had ypT₂ disease, 77 had ypT₃ disease, and 5 had ypT₄ disease. The rate of ypT₀ in 36 ypN (+) patients was significantly lower than that in 140 ypN₀ patients (3% vs. 35.1%, P = 0.000), yet its rate of RCCs in the subserosa/perirectal fat was significantly higher than that in ypN₀ patients (83% vs. 36.4%, P = 0.000). The rate of ypT₀ was significantly higher in 73 T₃ patients than in 102 T₄ patients (37% vs. 21.6%, P = 0.025). Conclusions: Most RCCs in the bowel wall of patients treated with preoperative VMAT with concurrent chemotherapy are distributed within or below the muscularis propria, which are significantly associated with ypT, ypN, and T stages. The value of biopsy for primary rectal lesions after neoadjuvant CRT may be very limited. (authors)