ORIGINAL ARTICLE Gender-Related Differences in Repopulation and Early Tumor Response to Preoperative Radiotherapy in Rectal Cancer Patients Anna Gasinska & Piotr Richter & Zbigniew Darasz & Joanna Niemiec & Krzysztof Bucki & Krzysztof Malecki & Andrzej Sokolowski Received: 4 March 2011 /Accepted: 10 June 2011 /Published online: 25 June 2011 # 2011 The Society for Surgery of the Alimentary Tract Abstract Purpose Inhibition of tumor proliferation rate based on bromodeoxyuridine labelling index (BrdUrdLI), S-phase fraction (SPF) and MIB-1 labelling index (MIB-1 LI) as an early rectal cancer response to preoperative radiotherapy (RT). Methods and materials A total of 122 patients qualified either for short RT (5 Gy/fraction/5 days) and surgery about 1 week after RT (schedule I) or for short RTand a 4-week interval before surgery (schedule II). Tumor samples were taken twice from each patient: before RTand at the time of surgery. In each sample, the BrdUrdLI, SPF and MIB-1 were calculated. Early tumor response was assessed by a biologist, a pathologist and surgeons. Results Fifty-six patients were treated according to schedule I and 66 patients according to schedule II. Mean BrdUrdLI, SPF and MIB-1 LI before RTwere 8.8%, 21.0% and 53.3%, respectively, and these values did not differ between the two compared groups. After RT, tumors showed statistically significant growth inhibition based on all assessed biological markers. As pretreatment assessed parameter was not predictive for early clinical and pathologic tumor response, prognostic role of the relative value (RV), that is, the ratio of assessed parameter after RT to before RT for each of the assessed markers, was considered. The ratios were calculated separately for fast and slowly proliferating tumors and separately for male and female patients. Fast proliferating tumors were more responsive. Differences with regard to sex were visible only in slowly proliferating tumors. Accelerated cell repopulation (4.8–28%/day) was noticed in female slowly proliferating tumors about 4 weeks after RT. Only for relative MIB-1 LI it was possible to show significant correlation with pathological tumor regression. Lack of such correlation for BrdUrdLI and SPF might reflect accelerated repopulation, particularly in slowly proliferating female tumors. Conclusions Accelerated repopulation was noticed in slowly proliferating tumors in females about 4 weeks after RT. A. Gasinska (*) : J. Niemiec Department of Applied Radiobiology, Center of Oncology, Garncarska 11, 31–115 Krakow, Poland e-mail: z5gasins@cyf-kr.edu.pl P. Richter Department of General Surgery, Jagiellonian University, Krakow, Poland Z. Darasz Department of Surgery, Center of Oncology, Krakow, Poland K. Bucki Collegium Medicum, Jagiellonian University, Krakow, Poland K. Malecki Department of Radiation Oncology, Center of Oncology, Krakow, Poland A. Sokolowski Department of Epidemiology, Center of Oncology, Krakow, Poland J Gastrointest Surg (2011) 15:1568–1576 DOI 10.1007/s11605-011-1589-4