Víctor Glen Ray López, Jesús Abrisqueta, Juan Antonio Luján, José Gil, Pascual Parrilla (Departments of Surgery, Hospital Clínico Universitario Virgen de la Arrixaca), Patrício Bernardo Lynn (Department of Surgery, New York University), Laura G. Frutos (Nuclear Medicine Radiology, Hospital Clínico Universitario Virgen de la Arrixaca), Eduardo J. Ortiz (Departments of Pathology, Hospital Clínico Universitario Virgen de la Arrixaca) and José Juan López (Center of Operations Research, Miguel Hernández University, Elche)
Abstract: Introduction: Rectoscopy and 18F-FDG PET/CT as a diagnostic algorithm for the assessment of tumor response in rectal cancer after neoadjuvant chemoradiation therapy (CRT) is very useful. Material and methods: This was a prospective longitudinal study in patients with locally advanced rectal cancer treated with neoadjuvant CRT. Patients were assessed after CRT completion with a digital rectal examination, proctoscopy and 18F-FDG PET/CT. Patients were subdivided as clinical (cCR) or radiologic (rCR) responders and non-responders according to tumor response. Clinical and radiological re-assessment was compared with the surgical specimen. Pathological tumor regression (pCR) grade was determined according to Mandard’s classification. Results: Of the 68 patients included, 15 (22 %) presented pCR in the surgical specimen and tumor persistence (non- PCR) was detected in the remaining 53 (78 %). Clinical assessment (DRE+ rectoscopy) identified 15 patients as cCR and 53 as non-cCR, two were false positives and two were false negatives. The overall accuracy was 94 %. 18F-FDG PET/CT identified 18 patients as rCR and 50 as non-rCR, one was a false positive and four were false negatives. The overall accuracy was 92 %. A combination of clinical findings and 18F-FDG PET/CT resulted in an accuracy of 96 %. The combination of clinical findings + 18F-FDG PET/CT was able to correctly identify all cases of pCR, with the exception of one case that presented a tumor regression of 80 %. Conclusion: In this series, 18F-PET-CT and clinical assessment had excellent accuracies in differentiating PCR from non-PCR after CRT completion. PET-CT combined with clinical assessment had a better accuracy than both modalities independently. 18F-FDG PET/CT is a valid tool that complements the clinical assessment of tumor response.