Transformation from Non-Small Cell to Small Cell carcinoma

Has anyone experienced stage IV NON-small cell carcinoma transforming to SMALL cell carcinoma? I received 4 cycles of chemo with Carboplatin and Pemetrexid then maintenance Pemetrexid for the NSCLC. Recent scans showed tumor progression to lung and liver. Liver biopsy showed my cancer had changed from non-small cell to small cell. I didn’t know that was possible. I’ll be starting 6 cycles of Cisplatin + Etoposide next week. My understanding is there are very limited treatment options for small cell carcinoma. Any experience or information you could share would be greatly appreciated.