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Under the traditional paradigm of genetic testing in cancer, the role of germline testing was to assess for the inherited risk of cancer, whereas the role of tumor testing was to determine therapeutic selection. Parallel tumor-normal genetic testing uses simultaneous genetic testing of the tumor and normal tissue to identify mutations and allows their classification as either germline or somatic. The increasing adoption of parallel testing has revealed a greater number of germline findings in patients who otherwise would not have met clinical criteria for testing. This result has widespread implications for the screening and further testing of at-risk relatives and for gene discovery. It has also revealed the importance of germline testing in therapeutic actionability. Herein, we describe the pros and cons of tumor-only versus parallel tumor-normal testing and summarize the data on the prevalence of incidental actionable germline findings. Because germline testing in patients with cancer continues to expand, it is imperative that systems be in place for the proper interpretation, dissemination, and counseling for patients and at-risk relatives. We also review new therapeutic approvals with germline indications and highlight the increasing importance of germline testing in selecting therapies. Because recommendations for universal genetic testing are increasing in multiple cancer types and the number of approved therapies with germline indications is also increasing, a gradual transition toward parallel tumor-normal genetic testing in all patients with cancer is foreseeable.

Lynch syndrome is a heritable cancer syndrome caused by a heterozygous germline mutation in DNA mismatch repair (MMR) genes. MMR-deficient (dMMR) tumors are particularly sensitive to immune checkpoint inhibitors, an effect attributed to the higher mutation rate in these cancers. However, approximately 15% to 30% of patients with dMMR cancers do not respond to immunotherapy. This report describes 3 patients with Lynch syndrome who each had 2 primary malignancies: 1 with dMMR and a high tumor mutational burden (TMB), and 1 with dMMR but, unexpectedly, a low TMB. Two of these patients received immunotherapy for their TMB-low tumors but experienced no response. We have found that not all Lynch-associated dMMR tumors have a high TMB and propose that tumors with dMMR and TMB discordance may be resistant to immunotherapy. The possibility of dMMR/TMB discordance should be considered, particularly in less-typical Lynch cancers, in which TMB evaluation could guide the use of immune checkpoint inhibitors.

Routine monitoring of carcinoembryonic antigen (CEA) levels is standard in patients with resected colorectal cancer (CRC). The incidence of false-positives and the upper limits of false-positive elevations have not been previously well characterized. A search of medical records at Memorial Sloan-Kettering Cancer Center identified 728 patients who underwent an R0 resection of locoregional CRC between January 2003 and December 2012 and who had an increase in CEA level above the normal range after a normal perioperative CEA level. Of these, 358 had a false-positive elevation of CEA level, 335 had a true-positive elevation indicative of recurrent CRC, and 35 had a true-positive elevation indicative of the development of a new, non-CRC malignancy. Of those with false elevations, 111 had a single isolated CEA level elevation (median highest CEA level of 5.5 ng/mL) with no further abnormal measurements, whereas 247 had elevations on 2 or more readings, with a median highest level of 6.7 ng/mL. Of these 247 patients with confirmed false-positive CEA level elevations, only 5 (2%) had measurements greater than 15 ng/mL, and no confirmed elevation greater than 35 ng/mL was a false-positive. False-positive CEA test results in the range of 5 to 15 ng/mL are common. Confirmation of CEA elevation in this range before initiating imaging studies may be appropriate. False-positive results greater than 15 ng/mL are rare, and all confirmed CEA levels greater than 35 ng/mL were associated with cancer recurrence.

Standard therapy for locally advanced rectal cancer (LARC) is preoperative chemoradiotherapy and postoperative chemotherapy. At Memorial Sloan-Kettering Cancer Center (MSKCC) the authors began offering FOLFOX (5-fluorouracil, leucovorin, and oxaliplatin) as initial treatment for patients with high-risk LARC to target micrometastases while treating the primary tumor. The purpose of this study is to report the safety and efficacy of initial FOLFOX given before chemoradiotherapy on tumor downsizing and pathologic complete response (pathCR) in LARC. The records of patients with stage II/III rectal cancer treated at MSKCC between 2007 and 2012 were reviewed. Of approximately 300 patients with LARC treated at MSKCC, 61 received FOLFOX as initial therapy. Of these 61 patients, 57 received induction FOLFOX (median 7 cycles) followed by chemoradiation, and 4 experienced an excellent response, declined chemoradiation, and underwent total mesorectal excision (TME). Twelve of the 61 patients did not undergo TME: 9 had a complete clinical response (CCR), 1 declined despite persistent tumor, 1 declined because of comorbidities, and 1 developed metastatic disease. Among the 61 patients receiving initial FOLFOX, 22 (36%) had either a pathCR (n=13) or a CCR (n=9). Of the 49 patients who underwent TME, all had R0 resections and 23 (47%) had tumor response greater than 90%, including 13 (27%) who experienced a pathCR. Of the 28 patients who received all 8 cycles of FOLFOX, 8 experienced a pathCR (29%) and 3 a CCR (11%). No serious adverse events occurred that required a delay in treatment during FOLFOX or chemoradiation. FOLFOX and chemoradiation before planned TME results in tumor regression, a high rate of delivery of planned therapy, and a substantial rate of pathCRs, and offers a good platform for nonoperative management in select patients.