2610 - Interim toxicity analysis for patients with limited stage small cell lung cancer (LSCLC) treated on the experimental thoracic radiotherapy (TRT) arms of CALGB 30610 (Alliance) / RTOG 0538

Background

The optimal TRT regimen for LSCLC remains to be defined. CALGB 30610/RTOG 0538 started as a 3 arm study designed to discontinue one of 2 experimental TRT arms based on interim toxicity assessment, while the remaining arm would be compared against standard 4500 cGy (twice-daily) TRT.

Methods

Per protocol, the interim endpoint was calculated based on treatment related grade 3+ non-hematologic toxicity, grade 4 hematologic toxicity, failure to complete 4 cycles of chemotherapy, and any grade 5 toxicity. The analysis included the initial 70 patients assigned to each of the 7000 cGy (once daily) and the 6120 cGy (concomitant boost) study arms. The initial analysis was conducted May 21, 2012 and an updated analysis of the same patient population was performed April 15, 2019.

Results

There was not a significant difference in toxicity scoring between the regimens, either in the 2012 assessment or the updated analysis. Overall grade 3, 4, and 5 treatment related adverse events were 21.4%, 54.3%, and 0% for 7000 cGy TRT compared with 20.0%, 57.1% and 1.4% for 6120 cGy TRT, while rates of non-hematologic toxicity were 10.0%. 12.9% and 0% for 7000 cGy TRT compared with 12.9%, 14.3%, and 1.4% with 6120 cGy TRT. Grade 3 pneumonitis was reported in 2 patients (2.9 %) in each cohort. Grade 4 dyspnea was observed in 4 patients (5.7 %) in the 6120 cGy cohort but was not reported in patients treated with 7000 cGy.

Conclusions

Both TRT regimens, 7000 cGy daily and 6120 cGy concomitant boost, concurrent with cisplatin and etoposide chemotherapy, appear to be tolerable without unexpected toxicity. A decision to discontinue the 6120 cGy arm in December 2012 was based on the toxicity distribution, as a significant difference in overall toxicity was not observed. Further details of toxicity and the scoring system applied will be presented. The phase III portion of the study comparing 7000 cGy TRT to 4500 cGy TRT is near completion.

Clinical trial identification

CALGB 30610 / RTOG 0538 Identifier: NCT00632853.

Editorial acknowledgement

Legal entity responsible for the study

Alliance for Clinical Trials in Oncology.

Funding

National Cancer Institute. Support: U10CA180821, U10CA180882, U10CA180868, U10CA180820, U10CA233330, U10CA180888; https://acknowledgments.alliancefound.org.

Disclosure

All authors have declared no conflicts of interest.