A divide-and-conquer strategy in tumor sampling enhances detection of intratumor heterogeneity in routine pathology: A modeling approach in clear cell renal cell carcinoma

Abstract

Intratumor heterogeneity (ITH) is an inherent process in cancer development which follows for most of the cases a branched pattern of evolution, with different cell clones evolving independently in space and time across different areas of the same tumor. The determination of ITH (in both spatial and temporal domains) is nowadays critical to enhance patient treatment and prognosis. Clear cell renal cell carcinoma (CCRCC) provides a good example of ITH. Sometimes the tumor is too big to be totally analyzed for ITH detection and pathologists decide which parts must be sampled for the analysis. For such a purpose, pathologists follow internationally accepted protocols. In light of the latest findings, however, current sampling protocols seem to be insufficient for detecting ITH with significant reliability. The arrival of new targeted therapies, some of them providing promising alternatives to improve patient survival, pushes the pathologist to obtain a truly representative sampling of tumor diversity in routine practice. How large this sampling must be and how this must be performed are unanswered questions so far. Here we present a very simple method for tumor sampling that enhances ITH detection without increasing costs. This method follows a divide-and-conquer (DAC) strategy, that is, rather than sampling a small number of large-size tumor-pieces as the routine protocol (RP) advises, we suggest sampling many small-size pieces along the tumor. We performed a computational modeling approach to show that the usefulness of the DAC strategy is twofold: first, we show that DAC outperforms RP with similar laboratory costs, and second, DAC is capable of performing similar to total tumor sampling (TTS) but, very remarkably, at a much lower cost. We thus provide new light to push forward a shift in the paradigm about how pathologists should sample tumors for achieving efficient ITH detection.

A multi-site cutting device implements efficiently the divide-and-conquer strategy in tumor sampling

“…When applied directly to the whole tumor surface previously thin-sliced, the grid will cut it into small cubes in one shot ( Figure 2 ). Next, the pathologist’s decision will consist simply in selecting the cubes that will be processed for analysis as previously reported 4 . The method can be applied (and has been tested) to both fresh and formalin-fixed tissue, saves time, and assures a uniform sampling distribution along the tumor.…”

“…We have designed the DAC strategy to enhance ITH detection in big tumors at the same cost 4 . For this reason, we propose to respect what the international protocols advice, that is, one cassette per centimeter of tumor diameter.…”

“…An experience-based reasoning says that this option will save pathologist’s time when handling large tumors, in a manner which is inexpensive and reliable at the same time. In combination with the changes proposed for the technician training in our previous report 4 , this new alternative will make the pathologists’ routine much faster and robust providing an integrated solution to fulfill basic researchers’ expectations 10 . If the DAC strategy is adopted as a suitable method to increase the amount of information given to oncologists, pathologist's routine will move from the classic big-fragments-into-the-cassette routine to a sort of rudimentary tissue microarray building, as recently proposed 4 .…”

“…This simple solution is based on the divide-and-conquer algorithm (DAC). Noteworthy, tumor sampling following DAC outperforms the routine protocol sampling for identifying ITH and, it does it, at a similar cost 4 . However, pathologists could consider that DAC is a time-consuming method when grossing, which might make it difficult to introduce it in routine practice.…”

“…We have recently proposed a reliable, affordable and time-saving solution to this problem 4 . The goal is twofold; to improve ITH detection and to perform ITH at affordable laboratory costs.…”