Differences between lung adenocarcinoma and squamous cell carcinoma in histological distribution of residual tumor after induction chemoradiotherapy.

Aims: To facilitate dose planning for convergent beam radiotherapy in non-small cell lung cancer (NSCLC), tumor response and histological distribution of residual tumors after induction chemoradiotherapy (ICRT) were compared between adenocarcinoma (AD) and squamous cell carcinoma (SQ).

Methods: Ninety-five patients with N1-2 or T3-4 NSCLC were treated with ICRT followed by surgery; 55 had AD and 40 had SQ. For the evaluation of distribution of residual tumors, the location of the external margin of residual tumors was assessed on surgical materials as follows: radius of whole tumor ("a"); distance between the center of tumor and the external margin of residual tumor ("b"); and its location ("b/a").

Results: Of the 55 AD cases, 8 (15%) showed pathological complete remission, which was significantly less frequent than 22 of 40 SQ cases (55%) (p < 0.001). AD showed the residual tumors at the most periphery of tumor (b/a = 1.0) more frequently than SQ, i.e., 39/55 (71%) versus 6/40 (15%), respectively (p < 0.001). Even in 65 cases other than the pathological complete remission, external margins in 47 AD cases located more periphery than those in 18 SQ cases, of which mean b/a values were 0.97 ± 0.17 and 0.70 ± 0.29, respectively (p < 0.001).

Conclusion: AD showed worse tumor response to ICRT than SQ. After ICRT, AD remained at the periphery of primary tumor more frequently than SQ. It seems that, also in the convergent beam radiotherapy, the periphery part of AD would be more resistant than that of SQ.