Dissection of primary prostate cancer to determine the clonal origin of synchronous lymph node metastasis.

Abstract

e17614 Background: Primary prostate cancer often consists of multiple, genomically-distinct clones. The clonal source of lymph node metastasis in multifocal disease is unknown. We sought to analyze and determine the histopathologic and molecular characteristics of the tumor sub-clones capable of metastasis in primary prostate cancers with synchronous lymph node metastasis. Methods: We identified patients with primary prostate cancer found to have lymph node (LN) metastasis at the time of radical prostatectomy, including those with multifocal disease. Punch biopsies were obtained from multiple regions of primary tumors and LN metastases. Targeted next generation sequencing to assess somatic DNA mutations, copy number alterations (CNA), and TMPRSS2:ERG fusion status. Bioinformatic analyses were performed using in-house developed pipelines. Phylogenetic evolutionary analyses were performed to delineate the primary cancer clone responsible for LN metastasis. Results: We identified 2 patients with LN cancer regions. In one patient, while all four Grade Group (GG) 5 primary tumor (PT) regions showed concordant TP53 and TPR non-synonymous mutations and broad copy number alterations (CNAs) with two LN foci, only two regions shared high level CNAs with both lymph node foci. In this case, a GG1 tumor focus showed no TP53 somatic mutation or CNA overlap with the high-grade tumor or lymph node samples. Critically, phylogenetic analysis revealed that the GG5 PT with extra-prostatic extension (EPE) showed higher concordance with the LN metastases than regions confined to the prostate. In another patient with four PT, phylogenetic analysis revealed that the PT with EPE closely resembled the LN metastasis; both were TMPRSS2:ERG fusion positive share PTEN copy number loss. Two PT (GG1 and 2) appeared to be independent clones and were TMPRSS2:ERG fusion negative. One of the six circulating tumor cells (isolated pre-prostatectomy) from this patient demonstrated a significant PTEN copy loss consistent with the findings in the region of EPE and the LN metastasis. Conclusions: Our findings confirm molecular heterogeneity of primary prostate cancers and homogeneity of LN metastases supporting the use of shared molecular alterations to infer clonal lineage. Our results highlight the critical role of adverse pathologic features, such as grade and EPE, in prostate cancer with synchronous lymph node metastasis.