NCCN has a variety of recommendations for second line therapy,all single agents, including irinotecan alone but not cisplatin/ irinotecan. Irinotecan and etoposide did not show any advantages over single agents. Amrubicin and topotecan seem to perform marginally better.
NCCN. Small Cell Lung Cancer, 2014
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Luo Q et al, Efficacy of different monotherapies in second-line treatment for small cell lung cancer: a meta-analysis of randomized controlled trials.Int J Clin Exp Med. 2015 Oct 15;8(10):19689-700.