OBJECTIVETo study the expression of myeloid-derived suppressor cells (MDSC) in peripheral blood of patients with rectal carcinoma and to preliminarily explore its clinical significance.

METHODSBlood samples from 76 rectal carcinoma patients who underwent surgery in Department of General Surgery, The Affiliated Cancer Hospital, Zhengzhou University between June and October 2013 were collected before operation, postoperative day 10 and 2 years after operation respectively. Flow cytometry was used to detect MDSC percentage in peripheral blood of 76 rectal carcinoma patients and 40 healthy people. The change of MDSC percentage in peripheral blood of rectal carcinoma patients after treatment was investigated. Furthermore, the relationship of peripheral blood MDSC percentage with clinicopathological characteristics was examined.

RESULTSPreoperative MDSC percentage in peripheral blood of 76 rectal carcinoma patients [(3.52±0.68)%] was higher than that of 40 healthy people[(0.92±0.21)%], with significant difference (t=3.026, P=0.005). Preoperative MDSC percentage in peripheral blood of rectal carcinoma patients was significantly related with histological classification (t=2.453, P=0.018), depth of tumor invasion (t=2.051, P=0.035), lymph node metastasis (t=2.328, P=0.022), TNM stage (t=2.529, P=0.016). Univariate analysis showed that TNM stage, histological classification, lymph node metastasis, preoperative MDSC percentage in peripheral blood were the prognostic factors in rectal carcinoma. Multivariate analysis showed that TNM stage (HR=2.535, 95%CI: 0.851 to 4.160, P=0.038) and preoperative MDSC percentage in peripheral blood (HR=3.651, 95%CI: 0.877 to 14.263, P=0.031) were independent prognostic factors of rectal carcinoma. MDSC percentage in peripheral blood of rectal carcinoma patients decreased significantly on the postoperative 10-day [(2.41±0.46)%] compared to that before operation [(3.52±0.68)%], whose difference was statistically significant (t=1.778, P=0.043). During follow-up, tumor recurrence or metastasis was found in 23 patients. MDSC percentage in peripheral blood of rectal carcinoma patients with recurrence or metastasis [(4.37±1.23)%] was higher than that of rectal carcinoma patients without recurrence or metastasis [(2.36±0.35)%] two years after operation, with statistically significant difference (t=1.982, P=0.039).

CONCLUSIONSMDSC percentage in peripheral blood of rectal carcinoma patients is significantly elevated compared to that of healthy people. Increased MDSC percentage indicates poor prognosis and tumor progression in rectal carcinoma patients. Measurement of peripheral blood MDSC percentage may have a potential clinical value in prognosis prediction of rectal carcinoma.