In one patient with a history of both primary prostatic adenocarcinoma and a metastatic lesion with small cell carcinoma/neuroendocrine features (TP1034/MO_1215), PRINCe assessment of synchronous (same-day) specimens detected a clear focal AR amplification in the cfDNA that was absent in the tissue based profiling of a prostatic neuroendocrine/small cell carcinoma focus (despite identical prioritized somatic point mutations), consistent with circulating evidence of both AR-driven and AR-independent clones (Figure 4A). The gene discussed is AR; the disease is small cell carcinoma.