Unless there is diagnostic uncertainty, ccRCC metastases are not sampled routinely. A proportion of synchronous metastases (e.g. lymph node, IVC thrombus or adrenal metastases) may be collected at surgery. When patients present with metachronous metastases, we frequently rely on the histological profile of the historical nephrectomy specimen. However, genotypes can be discordant between primary and metastases even with respect to VHL , and genetic alterations that drive disease progression and treatment resistance can arise de novo, or expand from a minor subclone, which evaded detection in the primary . These observations indicate that sampling of metastases and progressive disease sites could inform longitudinal changes in clonal dynamics especially in response to selective (treatment) pressure.
Available tumour profiling approaches range from single-gene tests and limited gene panel sequencing, to whole exome, transcriptome and whole genome sequencing. Although the latter have the advantage of being unbiased and include all the genic or even intergenic regions, their cost is prohibitive in routine clinical practice. As driver events in ccRCC, are relatively well defined bespoke gene panels, focused on the recurrently mutated genes copy number-altered regions could offer a compromise between the need for prognostic information and cost-effectiveness. These approaches reduce the burden on computational power and storage whilst affording a greater depth of sequencing. PCR-amplicon  and hybridization capture based methods are available with hybridization capture best suited for capture of larger target regions and exons from hundreds of genes .
It remains to be proven whether more extensive sampling and molecular profiling of ccRCC patients could determine the patient's prognosis and guide the clinical decision-making. To address this question, spatial and temporal sampling needs to be incorporated into clinical study design with histological and molecular profiling of tumours in a chronological sequence that starts with nephrectomy and concludes in postmortem sampling (Fig. 4). Integrated with robust clinical annotation of disease outcomes, such studies, already underway in lung cancer [59▪], would provide powerful biological insights but also practical guidance to disease management.
For small incidentally revealed renal masses (SRMs) (defined as <4 cm), active surveillance is an alternative to surgery for patients with significant comorbidities . Size is an important factor in determining the nature of renal masses. Approximately, 20% of renal masses less than 4 cm are ultimately found to be benign . However, another 20% may display poor prognostic features including high grade or invasion into the perirenal fat . Percutaneous biopsies are increasingly being used to support treatment decisions in this context [63,64]. Adverse genetic features such as BAP1 mutations could be used to stratify patients based on a molecular risk to either surgery or surveillance.
For locally advanced disease (T3 and T4), wherein open radical nephrectomy is the standard of care, there is divergent practice with respect to postoperative surveillance schedule, participation in adjuvant trials and the management of patients with lymph node, adrenal or vena cava involvement [65▪]. In the context of a prospective evaluation, multiregional sampling of the nephrectomy specimen would detect the presence of adverse genetic features and their clonal status and stratify the patients accordingly. Five-year survival for Stage III disease remains ∼54% almost entirely as a result of metastatic disease. Considering tumours that extend grossly into the vena cava or involve the regional lymph nodes, molecular profiling of these disease components could, in theory, anticipate the composition of future metastases and guide adjuvant therapy.
It has been speculated that cytoreductive nephrectomy has a role in the removal of the evolutionary sink . Although patients should continue to be selected on the current criteria for cytoreductive surgery , multiregional molecular profiling of nephrectomy specimens will show how the pruning of particular mutations affects future clonal dynamics and the long-term outcome. The most informative will be the longitudinal studies of paired nephrectomy-metastasis(es) to determine whether ccRCC metastasis occurs as separate waves of invasion from the primary tumour. Further, analyses of larger cohorts of primary-metastasis pairs could identify the origin of the metastatic subclone and its associated variants. Although only a small number of patients will be suitable for a metastectomy [65▪], tissue sampling should be sought in the remaining patients (biopsy or postmortem sampling) to facilitate these studies. Genomic profiling of metastatic sites could conceivably prioritise those that harbour treatment resistance-driving variants for surgical resection.
Recent studies have illuminated the clonal dynamics in ccRCC. By accepting the linear model of tumour evolution and investing ourselves in the concept of targeting single driver mutations, we had simplified our approach, thus limiting outcomes. ITH appears to be a consistent feature of this disease and should be considered in every aspect of its management from diagnosis, the use of prognostic and predictive tools, design of personalised treatment strategies and the stratification of patients into clinical trials. The clinical utility of molecular profiling throughout the course of disease and treatment can only be assessed in prospective trials that mandate serial tissue sampling. The success of such trials is critically dependent on all members of the multidisciplinary team, in particular oncologists, surgeons, radiologists and pathologists.
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