Introduction: Neoadjuvant radiochemotherapy (RCT) is the current standard for treatment of locally advanced rectal cancer aiming at downstaging the tumor and improvement of local recurrence rate. About one third of rectal cancer treated by this means, however, shows no regression. Current surgical research engages in the identification of this groups in advance. A mucinous component in rectal cancer represents a potential risk factor possibly associated with a decreased response. The aim of the study was to compare the response of mucinous and non-mucinous rectal cancer to neoadjuvant RCT.Patients & Methods: Patients with locally advanced rectal cancer (uT3/4N+) of the lower and middle third were treated with neoadjuvant RCT (54 Gy +5 FU). Local staging was standardized by means of rigid rectoscopy, rectal ultrasound and MRI. 6-8 weeks after completion of RCT standardized resection was performed (TME, AMI ligature and optional protective ileostomy). Patients were divided in mucinous (Group M +) and non-mucinous cancer (Group M-) by histology. Both groups were compared with regard to the grade of regression (Dworak), the postoperative pathological staging (pTN) and downstaging. Downstaging was defined as a reduction of T and N category in resection specimen vs. pretherapeutic staging (score: 1 point per change of T- and N-category).Results: 80 patients with rectal cancer treated with neoadjuvant RCT before surgery were included between 1999 and 2008. 15 patients had mucinous carcinoma (M+), 65 patients had no mucinous component (M-). There was no significant difference in age, sex, pretherapeutic staging (uTN) and pathological grading between the two groups. Tumor regression was significantly pronounced in group M+ compared to the group of mucinous rectal cancer patients (M-), whereas nodal status did not differ significantly (Table). A complete regression was found in 25% (Group M-) and in 10% (Group M+) (p = 0,003).Conclusion: The histologic subtype has an influence on the response of neoadjuvant RCT. Rectal cancer patients with a mucinous component have a worse response, as well as a lower degree of regression. If this should result in a less favorable prognosis, in future modified neoadjuvant therapeutic strategies might be considered for these easily identifiable patient group.

	ΔT(Pre-/post RCT)	ΔN(Pre-/post RCT)	Score ΔTN(Pre-/post RCT)	Regression grade	Grading
Group M-	0,95	0,55	1,50	3,00	2,31
Group M+	0,40	0,53	0,93	1,60	2,44
p-value	0,037	0.834	0,069	0,003	0,609

Differences in the scores of T and N categories between pre-and post-RCT staging (Delta T, Delta N und Delta TN), the post-RCT grading and the grade of regression (Dworak).