The standard of care in oncology has been genomic profiling of tumor tissue biopsies for the treatment and management of disease, which can prove to be quite challenging in terms of cost, invasiveness of procedure, and potential risk for the patient. As the number of available drugs in oncology continues to increase, so too does the demand for technologies and testing applications that can identify genomic alterations targetable by these new therapies. Liquid biopsies that use a blood draw from the diseased patient may offset the many disadvantages of the invasive procedure. However, as with any new technology or finding in the clinical field, the clinical utility of an analytical test such as that of the liquid biopsy has to be established. Here, we review the clinical testing space for liquid biopsy offerings and elucidate the technical and regulatory considerations to develop such an assay, using our recently validated PlasmaMonitorTM test.

Molecular profiling of urothelial cancers for therapeutic and prognostic potential has been very limited due to the absence of cancer-specific targeted therapies. We describe here 2 clinical cases with a histological diagnosis of an invasive sarcomatoid and a poorly differentiated carcinoma favoring urothelial with some neuroendocrine differentiation, two of the rarer types of urothelial cancers, which were evaluated for mutations in 212 genes for single-nucleotide variants and copy-number variants and 53 genes for fusions associated with solid tumors. In both cases, we identified variants in 2 genes, ARID1A and CDKN2A, indicative of the role of dysregulation of chromatin remodeling and cell cycle control as being common features of bladder cancer, consistent with the proposed model of tumorigenesis in these rare, highly aggressive pathological subtypes. The presence of a KRAS mutation in the poorly differentiated cancer and a TP53 mutation in the sarcomatoid tumor is indicative of a distinctive profile and adds a potential layer of molecular stratification to these rarer histological subtypes. We present a comparative analysis of the histological, clinical, and molecular profile of both cases and discuss the potential to delineate these tumors at the molecular level keeping in mind the possible therapeutic implications.

Patient derived xenograft (PDX) tumor models represent the closest step to in-human trials for cancer drug research and are therefore an invaluable resource. Implantation of a cancerous tissue from a patient's primary tumor directly into an immune-deficient mouse, generating a xenograft tumor potentially mimics the tumor microenvironment in the patient and allows for the evaluation of therapies specific to a particular tumor. One of the significant challenges associated with PDX tumors is the potential loss of the human component or the take-over by mouse tissue with every passage into a new mouse model. Short tandem repeats (STRs) are short intronic sequences of DNA that are highly polymorphic and contain a pattern of nucleotides repeated in tandem. STRs can be found in distinct regions of both prokaryotes and eukaryotes organisms, with each organism containing a unique combination of the STR allelic frequencies that allow for individuals to be unambiguously identified. STR analysis is routinely used to genotype PDX tumors comparative to the original resected human cancerous tissue, ensuring concordance with original tissue and to identify mouse tissue contamination with progressive passages. The Jackson Laboratory for Genomic Medicine's CLIA laboratory has evaluated over 170 PDX tumor samples from multiple mouse model passages across 105 diverse PDX mouse models. Of those samples analyzed, genomic DNA for 33 had been extracted from fresh frozen tissue and for 143 extracted from Formalin Fixed Paraffin embedded tissue (FFPE). The current study presents the challenges and discrepancies observed in our evaluation relative to number of passages for each tumor, sample type (FFPE vs fresh frozen) - reflective of tumor heterogeneity and also potential encroachment by mouse tissue. We also present results of a cross institutional comparative STR analysis study in 123 samples wherein discordance observed in certain cases were a result of differing sample types, suggestive that tumor heterogeneity can affect the STR results and could be a leading cause for cross institutional discordant genotyping results. Citation Format: Bridgette Sisson, Andrew Hesse, Melissa Soucy, Daniel Bergeron, Shelbi Burns, Kevin Kelly, Emily Jocoy, Margaret Bundy, Honey V. Reddi. Genotyping of patient-derived xenograft tumors using short tandem repeats: Challenges and observations in ensuring concordance across passages for effective preclinical studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1034.

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