Neoplastic mesorectal microfoci (MMF) following neoadjuvant chemoradiotherapy: Clinical and prognostic implications

Background: Neoplastic microfoci have frequently been found in the mesorectum, with poor outcome. In this study, incidence and clinical significance of mesorectal microfoci (MMF) were analyzed in patients operated on for rectal cancer following neoadjuvant chemoradiation. Methods: A case series of 68 patients with extraperitoneal rectal cancer treated with neoadjuvant chemoradiation and surgery (including total mesorectal excision) were investigated for presence of neoplastic MMF. Results: MMF were found in 26 cases (38.2%). Increasing incidence of microfoci was statistically related to pathologic involvement of the bowel wall (P = 0.0006), Mandard's tumor regression grading (P = 0.0006), and pathologic neoplastic mesorectal involvement (P < 0.00001). None of the nine patients with complete tumor disappearance displayed both microfoci and lymph node metastasis. Only one local recurrence developed in a patient with multiple MMF. One out of nine pT0 or TRG1 patients (11.1%) had distant metastases compared with 15 out of 59 pT1-4 or TRG2-5 (25.4%, P = 0.70). Conclusions: A remarkable incidence of MMF was found following chemoradiation. However, when this therapy induced complete regression of primary tumor (pT0-TRG1), we found that node metastases and neoplastic MMF also disappeared. These features should be confirmed to assess the impact of these microfoci in treatment decision making in rectal cancers. © 2006 Society of Surgical Oncology.