Tumor Heterogeneity as a Predictor of Response to Neoadjuvant Chemotherapy in Locally Advanced Rectal Cancer

Abstract

A standard therapy for locally advanced cancers includes neoadjuvant chemoradiation; however, currently there is no way of knowing which patients have disease that will respond to such therapy. We analyzed 21 pretreatment rectal cancer biopsy samples and found a positive correlation of the response to therapy with a quantitative mutant-allele tumor heterogeneity (MATH) score. This next-generation sequencing derived score may serve as a biomarker for response to therapy. Background: Neoadjuvant chemoradiotherapy (nCRT) is the standard of care for locally advanced adenocarcinoma of the rectum, but it is currently unknown which patients have disease that will respond. This study tested the correlation between response to nCRT and intratumoral heterogeneity using next-generation sequencing assays. Patients and Methods: DNA was extracted from formalin-fixed, paraffin-embedded biopsy samples from a cohort of patients with locally advanced rectal adenocarcinoma (T3/4 or N1/2 disease) who received nCRT. High read-depth sequencing of > 400 cancer-relevant genes was performed. Tumor mutations and variant allele frequencies were used to calculate mutant-allele tumor heterogeneity (MATH) scores as measures of intratumoral heterogeneity. Response to nCRT was pathologically scored after surgical resection. Results: Biopsy samples from 21 patient tumors were analyzed. Eight patients had disease noted to have complete response, 2 moderate, 4 minimal, and 7 poor. Higher MATH scores correlated with poorer response to treatment, demonstrating significantly increased tumor heterogeneity compared to complete response (P ¼ .039). Conclusion: The application of MATH scores as a measure of tumor heterogeneity may provide a useful biomarker for treatment response in locally advanced rectal cancer.

How to measure tumour response in rectal cancer? An explanation of discrepancies and suggestions for improvement

“…Yet, the innate genetic heterogeneity of rectal cancer leads to a variety of treatment responses [25][26][27] that can be recognised either with high resolution imaging techniques or in histological slides. Imaging does not require assessment of the resection specimens and hence can be repeated in vivo and compared sequentially.…”

Intra-tumoral genomic heterogeneity in rectal cancer: mutational status is dependent on preoperative biopsy depth and location.

“…A second possibility might be the application of whole exome sequencing or larger targeted gene panels (such as the TSO500, Illumina, San Diego, USA), as this possibly provides a more elaborate analysis of genomic mutations, as compared to next generation sequencing using a limited targeted gene panel. Using these techniques, the mutant-allele heterogeneity (MATH) score was developed to quantitatively assess the spread of allele frequencies, and has been correlated to response (19,33). However, as sampling errors are innate to the biopsy technique, parameters derived from full tumor imaging might be preferable to incorporate characteristics of all genetic sub clones present in these cancers.…”

“…KI-67, EGFR and P21) and genomic mutational status, as well as radiological parameters derived from MR and [ 18 F]FDG-PET/CT imaging (e.g. standardized uptake value (SUV) and apparent diffusion coe cient (ADC) (12)(13)(14)(15)(16)(17)(18)(19)(20). Unfortunately, these studies so far have not resulted in clinically used prediction models.…”

“…Furthermore, a high degree of intra-tumoral genomic heterogeneity (as investigated by whole exome sequencing) has been associated with worse disease-free survival and was correlated with a higher rate of liver metastases (26). So far, no speci c genomic mutations have been found to accurately predict response to neoadjuvant therapy in LARC patients (19).…”

Molecular and Kinetic Analyses of Circulating Tumor Cells as Predictive Markers of Treatment Response in Locally Advanced Rectal Cancer Patients

“…It has been reported that pCR after NCRT is associated with improved cancer outcome and significantly decreased rates of local recurrence. Conversely, the 40% non-response rate after NCRT [31] represents heterogeneity in response to standard treatment [32,33]. For the latter, new therapeutic strategies, avoidance of toxicity associated with ineffective treatment, and novel neoadjuvant chemotherapeutic options are needed [34,35].…”