OBJECTIVETo investigate the association of CD133 expression in rectal cancer tissues with neoadjuvant chemoradiotherapy (nCRT) and tumor regression grading (TRG) after nCRT.

METHODSRadical resected rectal cancer specimens and clinicopathological data of 105 patients, including 60 men and 45 women with median age of 59 years, diagnosed as locally advanced rectal cancer in Peking Union Medical College Hospital from January 2008 to December 2014 were collected retrospectively. Thirty-nine and 66 cases were histologically classified as good-moderate and poor differentiation respectively. Sixty-eight and 37 cases were clinically graded as stage I(-II( and III(-IIII( in preoperative assessment respectively. NCRT was administered in 61 cases before surgery (nCRT group). The nCRT consisted of preoperative pelvic radiotherapy using 50 Gy (2 Gy once, for 25 sessions) with FOLFOX regimen (5-fluorouracil plus oxaliplatin) for 2-3 cycles or XELOX regimen (capecitabine plus oxaliplatin) for 2 cycles. Patients underwent surgery after 6 courses of nCRT, and then received the same previous chemotherapy regimen. In nCRT group, biopsy specimens before nCRT were obtained in 45 cases. Forty-four cases received surgery alone without nCRT (surgery alone group). CD133 expression was tested by immunohistochemical Envision two-step methods. The histological TRG evaluation was performed in the nCRT group. TRG score 0-2 was defined as insensitivity to nCRT, whereas TRG score 3-4 was defined as sensitivity. CD133 expression in rectal cancer samples before and after nCRT was compared. Association of CD133 expression with TRG after nCRT was examined.

RESULTSNo significant differences of baseline parameters were found between nCRT group and surgery alone group (all P>0.05). The positive rate of CD133 in nCRT group was 70.4%(43/61,) which was significantly higher than that in surgery alone group (47.7%, 21/44)(χ(2)=5.566, P=0.018) and that in biopsy samples before nCRT group (44.4%, 20/45)(χ(2)=7.287, P=0.007). Twenty-two cases (36.1%, 22/61) in nCRT group had TRG score of 3-4 . Among these 22 cases, 11 cases were negative CD133, and constituted 61.1% (11/18) of all CD133-low expression cases in nCRT group, whereas the other 11 cases were positive CD133, and constituted 25.6%(11/43) of all CD133-high expression cases in nCRT group (χ(2)=6.974, P=0.008).

CONCLUSIONThe CD133 expression up-regulates markedly in rectal cancer after nCRT and nCRT may have potential positive modulation on CD133 expression. CD133-positive cancer reveals lower response to nCRT, suggesting CD133 may be a potential target for improving efficacy of nCRT in rectal cancer.