Assessment of a novel, full-thickness incisional biopsy model to restage rectal tumours after neoadjuvant chemoradiotherapy: results of an ex vivo pilot study

Methods: After surgical resection, 0.5 × 0.5 cm, full-thickness incisional biopsy was performed in 15 rectal cancers. Of these, 13 had RMA and 2 had mucosal cCR but a palpable intramural abnormality. In all patients, a full-thickness incisional biopsy was taken through the centre of these areas. The ypT stage of the incisional biopsy and the final total specimen were compared. Complete mucosal clinical response was deemed to have occurred when either no residual tumour or only a flat mucosal scar remained.

Results: Incisional biopsy correctly identified all patients that had been downstaged to ypT0; however, it also falsely identified 5 of 10 patients (50 %) with yp residual disease as ypT0. Overall performance of incisional biopsy to detect residual cancer was 50 % sensitivity, 100 % specificity, 100 % PPV, and 50 % NPV with an accuracy of 66 %. A complete mucosal clinical response occurred in only one of five patients downstaged to ypT0 (20 % sensitive). It also occurred in one patient, which was ultimately staged as ypT3.

Conclusion: This prospective data demonstrates that incisional biopsy is not suitable as a stand-alone method to restage rectal cancer after CRT. Alternate or complementary means of restaging are needed.

Background: There is currently no reliable means to restage rectal cancers after neoadjuvant chemoradiation. Recent histological evidence shows that the epicentre for residual cancer cells is focussed directly underneath any residual mucosal abnormality (RMA). This proof-of-concept study aimed to determine the utility of a novel, minimally invasive method of incisional biopsy as a restaging tool. A secondary aim was to compare its performance to clinical response assessment.