Factors associated with degree of tumour response to neo-adjuvant radiotherapy in rectal cancer and subsequent corresponding outcomes

Background

Tumour response to neo-adjuvant radiotherapy for rectal cancer varies significantly between patients, as classified by Tumour Regression Grade (TRG 0–3), with 0 equating to pathological complete response (pCR) and 3 denoting minimal/no response. pCR is associated with significantly better local recurrence rates and survival, but is achieved in only 20–30% of patients. The literature contains limited data reporting factors predictive of tumour response and corresponding outcomes according to degree of regression.

Methods

All patients with rectal cancer who received neo-adjuvant radiotherapy, entered into the National Cancer Database (NCDB) in 2009–2013, were included. Data were analysed on procedure performed, tumour details, pathological findings, chemo-radiotherapy regimens, patient demographics, outcomes and survival. Multivariate regression analysis was used to identify factors independently associated with pCR.

Results

Of 13,742 patients, 32.4% achieved pCR/TRG0 (4452). Factors associated with pCR (vs. TRG3) included adenocarcinoma rather than mucinous adenocarcinoma histology; well/moderately differentiated grade; lower clinical tumour (cT₁, cT₂, cT₃) and nodal (N₀ and N₁) stage, and the addition of neo-adjuvant chemotherapy. Elevated CEA levels were associated with TRG3. pCR patients had higher rates of local excision, shorter mean length of stay and lower unplanned readmission rates, than TRG3. R0 resection rates and overall survival were significantly higher in all grades of regression, compared to TRG3 (p < 0.0001).

Conclusion

Tumour regression correlates with outcomes. Identifying factors predictive of response may facilitate higher pCR rates, the tailoring of therapy, and improve outcomes.