Impact of Small Cell (SC) versus (vs.) Non-Small Cell (nSC) Morphology on Outcomes of Patients (pts) with Extra-Pulmonary, Poorly Differentiated Neuroendocrine Carcinoma (EP-PD-NEC)

Introduction: The 2018 SEER data indicates EP-PD-NEC morphology (SC vs. nSC) may impact patient outcomes. Aim(s): To explore differences in clinicalpathological/survival/treatment outcomes of SC vs. nSC EP-PD-NECs. Materials and methods: Multicentre data from pts with EP-PD-NEC for whom tumour tissue could be reviewed (2019 WHO) was retrospectively analysed. Results: 122 pts identified; Sc=50(40.9%)/nSC=72(59.1%), small/large bowel; SC=38.0%/nSC=26.4% (p=.233), stomach/oesophagus; SC=22.0%/nSC=11.1% (p=.130), pancreas/biliary; SC=22.0%/nSC=36.1% (p=.112), unknown primary; SC=16.0%/nSC=25% (p=.268). Distant metastasis at diagnosis; SC=80%/nSC=75% (p=.662), median age at diagnosis; SC=64yr/nSC=58.5yr (p=.098), male; SC=72%/nSC=61.1% (p=.248), smoking history; SC=48.8%/nSC=60.8% (p=.299), median Ki67%; SC=90%/nSC=80% (p=.001), Ki67>55%; SC=89.8%/nSC=73.2%(p=.036). 109(89.3%) pts had 1stline chemotherapy (CT) [commonest; platinum/etoposide (P/E)=76.1%, 5fluorouracil(5FU)-based=16.5%]. 1stline response rate (RR) and disease control rate (DCR) (any regimen); SC=57.5%/nSC=42.3% (p=.207), and SC=85%/nSC=65.4% (p=.054), respectively. 1stline P/E RR; SC=64.5%/nSC=35.9% (p=.030), 1stline P/E DCR; SC=90.3%/nSC=61.5% (p=.007). Median progression free survival (mPFS); SC=6.27 months(m)(95%CI;5.50-7.00)/nSC=4.8m(95%CI;3.82-5.78), p=.252, mPFS (1st line P/E); SC=6.27m(5.36-7.18)/nSC=4.30m(2.40-6.20), p=.231. Median overall survival; SC=20.53m(95%CI;13.44-27.61)/nSC=15.30m(95%CI;10.48-20.12), HR=1.147, p=.546 (on Cox-regression multivariable analysis; HR=1.304, p=.272). Conclusion: nSC (compared to SC) EP-PD-NECs have a lower Ki67 and are less likely to respond to P/E, and may benefit from different 1stline CT.