Citations

e15030 Background: Deficiencies in the DNA mismatch repair (dMMR) system cause errors during DNA replication, which in turn give rise to microsatellite instability (MSI-H). MSI-H in mCRC is rare and its prognostic and predictive impact on outcome is unclear. This cohort study aims to investigate the prognostic and predictive value of MSI-H in metastatic CRC prior to the immune therapy era. Methods: 75 MSI-H mCRC patients (pts) and 75 matched (age, gender, disease sidedness, metachronous) MSS mCRC pts were identified from 1268 mCRC who had MSI/MMR test results at Mayo Clinic Rochester between 1/1992 and 7/2016. A retrospective review was conducted by using data from electronic medical records (EMR). Statistical analyses utilized Kaplan-Meier method, Log-rank test, and Cox proportional hazards models. Results: In the MSI-H group, there were 39 male (52%) and 36 female (48%) pts. Median age at metastatic disease diagnosis was 54.7 years. 35 patients presented with stage IV CRC. Primary tumors location: 38 right side, 11 transverse colon, 15 left side, 11 rectum. The MSS group was well matched (3 mismatches for gender and 1 mismatch for metachronous metastatic disease). Median overall survivals (OS) were 28.1 and 37.4 months for MSI-H and MSS pts, respectively ( p= 0.098). 98.7% MSS pts and 94.7% MSI-H pts had Fluoropyrimidine-based chemotherapy for metastatic disease and there was no median OS difference between these two groups (37.4 vs. 32.3 months p= 0.91). 43 MSI-H and 39 MSS pts had metastasectomy including ablation ( p= 0.51) with longer median OS (82.0 and 69.9 months, p= 0.90) compared to pts without metastasectomy (13.9 and 19.7 months, p= 0.15). Age < 65, metastasectomy, asymptomatic metastatic lesions, BRAF wild type, and multiple metastasectomy were associated with better survival in univariate analysis. Only metastasectomy remained statistically significant in multivariate analysis ( p< 0.0001). Conclusions: MSI-H mCRC do not appear to have improved prognosis compared with MSS cancers, in fact, there is a trend toward inferior outcome. In both groups, metastasectomy including multiple metastasectomy should be considered to optimize OS.

3556 Background: To define and update survival rates and relapse patterns in patients (pts) with isolated advanced abdominal nodal metastasis secondary to colorectal cancer (CRC), treated with curative intent using aggressive trimodality therapy. Methods: Fifty-seven pts with isolated advanced abdominal lymph node metastasis (retroperitoneal and mesenteric) secondary to colorectal cancer received trimodality therapy defined as chemotherapy delivered in conjunction with external beam radiotherapy (EBRT) followed by lymphadenectomy and intraoperative radiotherapy (IORT). Infusional 5-FU was the most common radiosensitizer used (66%, 38 pts). The median dose of EBRT was 50 Gy & the median dose of intraoperative radiotherapy was 12.5 Gy. End points included distant metastasis, toxicities, local failure within EBRT field, recurrence within the intraoperative radiotherapy field, and survival. Results: 49% of pts were male, median age 50.5 yrs. All patients had ECOG ≤ 1. 27 pts had primary right sided colon cancer, 16 left sided colon cancer and 14 rectal primaries. Median time from initial CRC diagnosis to development of abdominal lymph node metastatic disease was 24 months (95% CI, 23.5-45.1 months). 84% (48 pts) had paraaortic nodal metastases, 12% (7 pts) had mesenteric nodal metastases, and 3% (2 pts) had both. With a median follow up of 89.4 months, the median overall survival and 5-year estimated survival rate were 53.2 months (95% CI, 46.4-78.8 months) and 42%, respectively. Median progression free survival was 19.3 months (95% CI, 15.6-32.8 months). 21 (37%) pts never developed distant disease. Outcome was not affected by disease sidedness, rectal primary, or mutational profile. Treatment was well tolerated without any grade 3/4 toxicities. Conclusions: The use of trimodality therapy including EBRT with radiosensitizing chemotherapy, lymphadenectomy and IORT produces sustainable long-term survival in selected metastatic CRC pts presenting with isolated retroperitoneal/mesenteric nodal relapse.

Abstract Background Deficiencies in the DNA mismatch repair system cause errors during DNA replication, which in turn give rise to microsatellite instability (MSI). The impact of MSI on survival in metastatic colorectal cancer (mCRC) is unclear. This cohort study aims to investigate the prognostic and predictive value of MSI in mCRC prior to the immune therapy era. Materials and Methods A total of 75 MSI-high (MSI-H) mCRC patients (pts) and 75 matched (age, gender, disease sidedness, metachronous/synchronous) microsatellite-stable (MSS) mCRC pts were identified from 1,268 mCRC pts who had MSI/mismatch repair test results at Mayo Clinic Rochester between January 1992 and July 2016. A retrospective review was conducted by using data from electronic medical records. Statistical analyses utilized the Kaplan-Meier method, log-rank test, and Cox proportional hazards models. Results The MSS group was well matched to the MSI-H group based on age, gender, location, and chronicity of metastatic disease. MSI-H mCRC pts had earlier disease recurrence (median time from initial diagnosis to metastatic disease diagnosis, MSI-H group 12.9 vs. MSS group 20.9 months, p = .034). Median overall survival (OS) was 28.1 and 37.4 months for MSI-H and MSS pts, respectively (p = .99). In total, 94.7% of MSI-H pts and 98.7% of MSS pts had fluoropyrimidine-based chemotherapy for metastatic disease, and there was no difference in OS between these two groups (32.3 vs. 37.4 months, p = .91). Forty-three MSI-H and thirty-nine MSS pts had metastasectomy and/or ablation of metastases (p = .51) with longer median OS compared with pts without metastasectomy (MSI-H: 82.0 vs. 13.9, p &lt; .001; MSS: 69.9 vs. 19.7, p &lt; .001). Age &lt;65 years, BRAF wild type, and metastasectomy were associated with better OS in univariate analysis. Only metastasectomy remained statistically significant in multivariate analysis (p &lt; .001). Conclusion In mCRC, patients with MSI-H tumors have similar, but numerically shorter, median overall survival compared with those with MSS tumors. In both groups, metastasectomy and ablation of metastatic disease should be considered to optimize OS. Implications for Practice This study clearly demonstrated the survival benefits that aggressive metastasectomy provides in selected microsatellite instability-high metastatic colorectal cancer patients. This could be meaningful practice-changing information that has been long awaited.

Abstract Background The purpose of this study was to define survival rates in patients with isolated advanced abdominal nodal metastases secondary to colorectal cancer (CRC), treated with curative-intent trimodality therapy. Materials and Methods Sixty-five patients received trimodality therapy, defined as chemotherapy delivered with external beam radiotherapy (EBRT) followed by lymphadenectomy and intraoperative radiotherapy (IORT). Infusional 5-fluorouracil was the most common radiosensitizer used (63%, 41 patients). The median dose of EBRT was 50 Gy, and the median dose of IORT was 12.5 Gy. We evaluated time to distant metastasis, toxicities, local failure within the EBRT field, recurrence within the IORT field, and survival. Results Fifty-two percent of patients were male; patients’ median age was 50.5 years. All patients had an Eastern Cooperative Oncology Group score ≤1. Twenty-nine patients had right-sided colon cancer, 22 had left-sided colon cancer, and 14 had rectal primaries. The median time from initial CRC diagnosis to development of abdominal nodal metastatic disease was 20.6 months (95% confidence interval [CI], 21.2–40.8 months). Seventy-eight percent (51 patients) had para-aortic nodal metastases, 15% (10 patients) had mesenteric nodal metastases, and 6% (4 patients) had both. With a median follow-up of 77.6 months, the median overall survival and 5-year estimated survival rate were 55.4 months (95% CI, 47.2–80.9 months) and 45%, respectively. The median progression-free survival was 19.3 months (95% CI, 16.5–32.8 months). Twenty-six (40%) patients never developed distant disease. The outcome was not affected by disease sidedness or rectal primary. Treatment was well tolerated without grade 3 or 4 toxicities. Conclusion Trimodality therapy produces sustainable long-term survival in selected patients with metastatic CRC presenting with isolated retroperitoneal or mesenteric nodal relapse. Implications for Practice This article reports a unique trimodality approach incorporating external beam radiotherapy with radiosensitizing chemotherapy, surgical resection, and intraoperative radiotherapy provides durable survival benefit with significant curative potential for patients with metastatic colorectal cancer who present with isolated abdominal nodal (mesenteric and/or retroperitoneal) recurrence.

Abstract Background BRAF V600E mutations are present in 8%–10% of patients with metastatic colorectal cancer (mCRC) and portend poor prognosis. This study investigated the impact of metastasectomy for patients with BRAF V600E mCRC. Subjects, Materials, and Methods Using prospective clinical and molecular data, patients with BRAF V600E mCRC were analyzed for clinical characteristics and survival. Statistical analyses utilized the Kaplan-Meier method, log-rank test, and Cox proportional hazard models. Results Fifty-two patients were identified between July 1, 2008, and January 4, 2016. Patient characteristics included median age 65 years, 61% female, Eastern Cooperative Oncology Group performance status ≤1, 71% with right-sided tumors, and 28% with liver-limited metastasis. In the first-line setting, 7% (4/52) received fluorouracil, leucovorin, oxaliplatin, and irinotecan (FOLFOXIRI)/bevacizumab (BEV) and 81% were treated with doublet chemotherapy consisting of fluoropyrimidine, oxaliplatin, and BEV. Median overall survival (OS) for all 52 patients was 25 months with median progression-free survival (PFS) of 9.3 months. With median follow-up of 18.3 months, 21 patients underwent metastasectomy with longer OS (29.1 months vs. 22.7 months, hazard ratio [HR] = 0.33; confidence interval [CI], 0.12–0.78; p = .01) and PFS (13.6 months vs. 6.2 months, HR = 0.53, CI, 0.28–0.97; p = .03) compared with the non-metastasectomy cohort. In multivariate analysis, metastasectomy remained significant for improved survival outcomes (HR = 0.52; 95% CI, 0.07–1.02; p = .02). Median disease-free survival after metastasectomy was 9.7 months (95% CI, 5.5–19.5). Two patients remain disease-free at the time of last follow-up, with one patient without relapse for greater than 2 years (28.9 months). Conclusion Multimodality therapy incorporating metastasectomy for BRAF V600E mCRC should be considered and might be associated with improved overall survival in select patients. Implications for Practice BRAF V600E metastatic colorectal cancer (mCRC) represents an extremely difficult molecular subset of colorectal cancer to treat. To date, this subset remains refractory to standard chemotherapies, prompting extensive clinical investigation regarding novel treatment approaches and targeted modalities. While the use of metastasectomy for expanded RAS wild-type and RAS mutated mCRC has resulted in improved overall survival for select patients, utilization of metastasectomy in patients with BRAF V600E mCRC remains controversial. This article explores the authors' experience with BRAF V600E mCRC to ascertain whether a multidisciplinary approach incorporating metastasectomy for well-selected patients improves overall survival.