Background: Neoadjuvant chemoradiation therapy (nCRT) for rectal cancer may lead to cure. As we currently lack reliable methods to clinically confirm the absence of disease, some patients undergo radical resection and have pathological complete response (pCR) still undergo surgery. Furthermore, it is uncertain if conventional one-level histopathological analysis is accurate enough to determine complete response. Confirming pCR is essential to determine the prognosis and to consider the patient's inclusion in trials of adjuvant therapy. The aim of this study was to determine whether the current 1-level approach is sufficient to confirm pCR.
Methods: Four hundred and thirty-five patients with rectal cancer who received nCRT followed by radical resection were analyzed. All cases identified as pCR by 1-level step section histological evaluation were reassessed with 3-level step sections and immunohistochemical analysis to verify the presence of residual disease.
Results: Out of 435 patients, 75 (17.2%) were staged as ypT0. Of these, 6 had lymph node involvement and 1 had distant metastasis, leaving 68 (15.6%) who had pCR. After the additional step sections, residual tumor was detected in 12 (17.6%) of these 68. The final pCR rate was 12.9%. Distant recurrence was detected in 7.1% of real-pCR patients compared to 16.7% in the false-pCR group (p = 0.291). Sensitivity of clinical assessment for detecting pCR was 35.7%, and the accuracy of 1-section histological evaluation to identify pCR was 82.4%.
Conclusions: Histopathological analysis with 1-level step section is insufficient to determine complete tumor eradication. The 3-level sections methodology revealed residual tumor cells in patients initially classified as ypT0. Further studies with larger sample size are required to verify the clinical relevance of these residual tumor cells. Caution should continue to be applied to watch and wait strategies following nCRT.
Keywords: Complete response; Neoadjuvant therapy; Pathologic response; Rectal cancer; Watch and wait.