The efficacy of neoadjuvant radiotherapy in patients with signet ring cell carcinoma of the rectum: a retrospective case control study

Introduction: Signet ring cell carcinoma of the rectum (SRCCR) is a rare rectal tumor, therefore, only limited information is available on the management of patients with this diagnosis. Since literature data on the susceptibility of signet ring cell carcinoma to radiation therapy (RT) are controversial, one of the questions that specialists may have is whether the RT is effective as the first stage of treatment. Materials and methods: We conducted a retrospective analysis of medical records of patients with SRCCR treated at Research Institute FSBI «N. N. Blokhin Oncology Center» of the Ministry of Health of Russia from 1998 to 2020. The inclusion criteria were as follows: histologically confirmed primary SRCCR, disease stage I-III, use of RT or chemoradiotherapy at the first stage. A case control study design was used to select a control group of patients with rectal adenocarcinoma, and each case of the control group was compared with the study group by the following criteria: the year of treatment, the cT and cN clinical stage, the use of RT or CRT. The main endpoint was the rate of Dworak tumor regression grade 3-4; secondary endpoints included 5-year overall survival (OS) and progression-free survival (PFS) rates. Results: The study and control groups included 16 patients each. In each group, 14 (87,5%) patients received CRT and 2 (12,5%) received RT; cT3, cT4 stages were diagnosed in 7 (43,8%) and 9 (56,3%) patients, respectively; cN0 and cN1-2 stages were diagnosed in 3 (18,8%) and 13 (81,2%) patients, respectively. Eight (50%) patients in the SRCCR group and 4 (25,0 %) patients in the control group had Dworak tumor regression grade 3-4 (p = 0.273), and one (6,3 %) patient in each group showed pathological complete response (p > 0.99). The 5-year OS in the SRCCR group and the control group was 34,9% and 51,4%, respectively (p = 0.833); the 5-year PFS was 30,8% and 35,6%, respectively (p = 0.094). Conclusions: SRCCR is at least as susceptible to RT / CRT as rectal adenocarcinoma, for which neoadjuvant RT / CRT is the standard of care; the use of combination therapy produces comparable long-term results.