Operative technique: Pectoralis major flap with rib

The osteomyocutaneous pectoralis major flap was first described in 1980 and provides a single stage reconstructive option for poor free flap or pectoralis major flap with reconstruction plate candidates requiring bony reconstruction. The flap provides good functional and cosmetic outcomes in appropriately selected patients. We describe the indications and operative techinique for harvesting this flap in written and video format.

Therapeutic implications of germline vulnerabilities in DNA repair for precision oncology

DNA repair vulnerabilities are present in a significant proportion of cancers. Specifically, germline alterations in DNA repair not only increase cancer risk but are associated with treatment response and clinical outcomes. The therapeutic landscape of cancer has rapidly evolved with the FDA approval of therapies that specifically target DNA repair vulnerabilities. The clinical success of synthetic lethality between BRCA deficiency and poly(ADP-ribose) polymerase (PARP) inhibition has been truly revolutionary. Defective mismatch repair has been validated as a predictor of response to immune checkpoint blockade associated with durable responses and long-term benefit in many cancer patients. Advances in next generation sequencing technologies and their decreasing cost have supported increased genetic profiling of tumors coupled with germline testing of cancer risk genes in patients. The clinical adoption of panel testing for germline assessment in high-risk individuals has generated a plethora of genetic data, particularly on DNA repair genes. Here, we highlight the therapeutic relevance of germline aberrations in DNA repair to identify patients eligible for precision treatments such as PARP inhibitors (PARPis), immune checkpoint blockade, chemotherapy, radiation therapy and combined treatment. We also discuss emerging mechanisms that regulate DNA repair.

Abstract 349: Association of DNA damage response capacity with neoadjuvant chemoradiation response in locally advanced rectal cancer

Background: Locally advanced rectal cancer (RC) cases are ~60% of newly diagnosed RCs, with neoadjuvant chemoradiation therapy (nCRT) followed by surgery as the standard of care. While nCRT is highly toxic, it is also beneficial. Recent prospective trials reported that up to 59% locally advanced RC cases exhibit complete clinical response, suggesting these patients as ideal candidates for organ preservation. However, currently there is no biomarker to predict who will or will not benefit from nCRT. The goal of this study was to establish a predictive biomarker for benefit from nCRT, based on the hypothesis that inherent DNA damage response (DDR) capacity contributes to nCRT response in RC.

Methods: To gain insight into inherent DDR capacity, we profiled primary peripheral blood lymphocytes (pPBLs) from RC patients by quantitative immunofluorescence, Luminex-multianalyte assay, and pPBL DNA whole exome sequencing (WES). RC patients analyzed were segregated by neoadjuvant rectal (NAR) score: NAR<1, complete responders (CRs), n=21; NAR>14, poor responders (PoRs), n=21; 1<NAR<14, partial responders (PRs), n=12. Conditional inference trees were used to establish optimal cut points for the nCRT response outcomes data. Single nucleotide variants from WES data were annotated and analyzed for variation in genes involved in DDR, and associated pathways. The variants were annotated as predicted-pathogenic based on the consensus of four variant effect prediction programs.

Results: pPBLs from CRs showed significantly elevated γH2AX foci (a hallmark of double strand breaks) vs. PoRs (P<0.001, Kruskal-Wallis test). Multianalyte DDR panel testing revealed significantly increased expression or activation of 6 DDR proteins (ATR, MDM2, phosphorylated H2AXS139 (γ), p53S15, Chk1S345, and Chk2T68) in pPBLs from CRs versus PoRs (p<0.01, logistic regression model) and significantly increased protein levels of 4 DDR proteins (ATR, MDM2, p53S15, Chk2T68) in pPBLs from CRs vs. pPBLs from PRs (p<0.05, logistic regression model). We generated a combined DDR Score which positively and significantly correlated with CR vs. PoR (P<0.001, ordinal logistic regression model). From the combined DDR score, using mean score >0.082 as a cutpoint, we could include 90% patients with a CR. Finally, WES analysis of pPBL DNA from 15 CRs and 15 PoRs revealed that CRs were enriched in predicted-pathogenic variants in base excision repair genes vs. PoRs (p<0.01, q<0.025, FDR).

Conclusion and future work: Overall, our data suggests inherent DDR capacity testing may predict the magnitude of benefit from nCRT and assist in patient selection for treatment. Validation in a larger RC patient population is needed to confirm these findings. Biological studies testing the impact of the identified variants in base excision repair on inherent DDR capacity are warranted.

Citation Format: Elena V. Demidova, Randy W. Lesh, Vladimir Avkshtol, Margret B. Einarson, Erica A. Golemis, Sanjeevani Arora, Joshua E. Meyer. Association of DNA damage response capacity with neoadjuvant chemoradiation response in locally advanced rectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 349.

Prevalence of pathogenic variants in DNA damage response and repair genes in patients undergoing cancer risk assessment and reporting a personal history of early-onset renal cancer

Pathogenic variants (PVs) in multiple genes are known to increase the risk of early-onset renal cancer (eoRC). However, many eoRC patients lack PVs in RC-specific genes; thus, their genetic risk remains undefined. Here, we determine if PVs in DNA damage response and repair (DDRR) genes are enriched in eoRC patients undergoing cancer risk assessment. Retrospective review of de-identified results from 844 eoRC patients, undergoing testing with a multi-gene panel, for a variety of indications, by Ambry Genetics. PVs in cancer-risk genes were identified in 12.8% of patients—with 3.7% in RC-specific, and 8.55% in DDRR genes. DDRR gene PVs were most commonly identified in CHEK2, BRCA1, BRCA2, and ATM. Among the 2.1% of patients with a BRCA1 or BRCA2 PV, < 50% reported a personal history of hereditary breast or ovarian-associated cancer. No association between age of RC diagnosis and prevalence of PVs in RC-specific or DDRR genes was observed. Additionally, 57.9% patients reported at least one additional cancer; breast cancer being the most common (40.1% of females, 2.5% of males). Multi-gene testing including DDRR genes may provide a more comprehensive risk assessment in eoRC patients. Further validation is needed to characterize the association with eoRC.

Existing and Emerging Biomarkers for Immune Checkpoint Immunotherapy in Solid Tumors

In the last few years, immunotherapy has transformed the way we treat solid tumors, including melanoma, lung, head neck, breast, renal, and bladder cancers. Durable responses and long-term survival benefit has been experienced by many cancer patients, with favorable toxicity profiles of immunotherapeutic agents relative to chemotherapy. Cures have become possible in some patients with metastatic disease. Additional approvals of immunotherapy drugs and in combination with other agents are anticipated in the near future. Multiple additional immunotherapy drugs are in earlier stages of clinical development, and their testing in additional tumor types is under way. Despite considerable early success and relatively fewer side effects, the majority of cancer patients do not respond to checkpoint inhibitors. Additionally, while the drugs are generally well tolerated, there is still the potential for significant, unpredictable and even fatal toxicity with these agents. Improved biomarkers may help to better select patients who are more likely to respond to these drugs. Two key biologically important predictive tissue biomarkers, specifically, PD-L1 and mismatch repair deficiency, have been FDA-approved in conjunction with the checkpoint inhibitor, pembrolizumab. Tumor mutation burden, another promising biomarker, is emerging in several tumor types, and may also soon receive approval. Finally, several other tissue and liquid biomarkers are emerging that could help guide single-agent immunotherapy and in combination with other agents. Of these, one promising investigational biomarker is alteration or deficiency in DNA damage response (DDR) pathways, with altered DDR observed in a broad spectrum of tumors. Here, we provide a critical overview of current, emerging, and investigational biomarkers in the context of response to immunotherapy in solid tumors.