Genomic Complexity Predicts Resistance to Endocrine Therapy and CDK4/6 Inhibition in Hormone Receptor-Positive (HR+)/HER2-Negative Metastatic Breast Cancer

PURPOSE

Clinical biomarkers to identify patients unlikely to benefit from CDK4/6 inhibition (CDK4/6i) in combination with endocrine therapy (ET) are lacking. We implemented a comprehensive circulating tumor DNA (ctDNA) analysis to identify genomic features for predicting and monitoring treatment resistance.

EXPERIMENTAL DESIGN

ctDNA was isolated from 216 plasma samples collected from 51 patients with hormone receptor-positive (HR+)/HER2-negative (HER2-) metastatic breast cancer (MBC) on a phase II trial of palbociclib combined with letrozole or fulvestrant (NCT03007979). Boosted whole-exome sequencing (WES) was performed at baseline and clinical progression to evaluate genomic alterations, mutational signatures, and blood tumor mutational burden (bTMB). Low-pass whole-genome sequencing was performed at baseline and serial timepoints to assess blood copy-number burden (bCNB).

RESULTS

High bTMB and bCNB were associated with lack of clinical benefit and significantly shorter progression-free survival (PFS) compared with patients with low bTMB or low bCNB (all P < 0.05). Dominant APOBEC signatures were detected at baseline exclusively in cases with high bTMB (5/13, 38.5%) versus low bTMB (0/37, 0%; P = 0.0006). Alterations in ESR1 were enriched in samples with high bTMB (P = 0.0005). There was a high correlation between bTMB determined by WES and bTMB determined using a 600-gene panel (R = 0.98). During serial monitoring, an increase in bCNB score preceded radiographic progression in 12 of 18 (66.7%) patients.

CONCLUSIONS

Genomic complexity detected by noninvasive profiling of bTMB and bCNB predicted poor outcomes in patients treated with ET and CDK4/6i and identified early disease progression before imaging. Novel treatment strategies including immunotherapy-based combinations should be investigated in this population.

Abstract PS2-09: Next generation sequencing (NGS) in older adults with breast cancer using tissue-based and circulating tumor DNA (ctDNA) assays

Background: With advances in next generation sequencing (NGS) and now approved targeted therapy in breast cancer, genomic testing to identify potentially actionable mutations has become a common practice in patients (pts) with advanced breast cancer using both ctDNA and traditional tissue-based assays. Less is known regarding physician practice patterns in obtaining NGS testing and the practical implications of testing in older adults with breast cancer.Methods: Pts with advanced breast cancer underwent molecular profiling using a plasma-based ctDNA NGS assay (Guardant360® or Tempus®) between 5/2015 and 5/2020 at Siteman Cancer Center. Pts with advanced breast cancer who underwent genomic profiling using a tissue-based NGS assay (Tempus®) between 12/2017 and 5/2020 at this institution were also included. Clinicopathological histories were obtained from the medical record. Correlations were examined using a Fisher’s exact test.Results: During 5/15-5/20, 244 pts underwent ctDNA testing and 147 pts had a tissue-based NGS assay performed. There was no significant difference between the number of pts ≥ 65 years-old who underwent ctDNA testing (n=78, 32.0%) and tissue testing (n=37, 25.2%). There was no statistically significant difference between date of metastatic diagnosis and date of NGS testing between the older and younger cohorts. In pts who underwent tissue-based NGS testing, there was no significant difference between site of tissue tested (distant recurrence vs local) in the older and younger cohorts. The most common clinical managements following both ctDNA and tissue-based testing are presented in Table 1. Out of the 391 pts who underwent testing, 27 pts had both ctDNA and tissue-based NGS performed. Pts ≥ 65 were less likely to have both assays performed (n=3, 11.1%; p&lt;0.05). In pts undergoing both assays, there were high concordance rates of ESR1 (81.5%) and PIK3CA (81.5%) mutations. Mean time between tissue and plasma collection for NGS testing in pts undergoing both assays was 356.4 days.

Conclusion: Older adults, who are typically less likely to be included in clinical trials, may still benefit from NGS to reveal potentially targetable mutations. It is reassuring in our cohort that older adults had ctDNA and tissue-based NGS performed at similar rates as part of standard of care treatment. The clinical management following NGS testing was also not significantly different in the older adult cohort. Older adults were less likely to have both tissue and ctDNA testing performed however, given the high concordance rates between tests, this may be less clinically relevant.

Table 1clinical management following NGS testing≥65 years-old&lt;65 years-oldp valueno actionable mutations41 (35.7%)123 (44.6%)p=0.1testing results saved for potential future use27 (23.5%)45 (16.3%)p=0.1change in management15 (13.0%)41 (14.9%)p=0.6

Citation Format: Katherine K Clifton, Jingqin Luo, Yu Tao, Jennifer Saam, Thereasa Rich, Timothy Rearden, Anna Roshal, Ashley Frith, Caron Rigden, Foluso Ademuyiwa, Katherine Weilbaecher, Leonel Hernandez Aya, Lindsay Peterson, Nusayba Bagegni, Rama Suresh, Ron Bose, Tanya Wildes, Mateusz Opyrchal, Cynthia Ma. Next generation sequencing (NGS) in older adults with breast cancer using tissue-based and circulating tumor DNA (ctDNA) assays [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS2-09.

Nanoparticle albumin-bound paclitaxel with cetuximab and carboplatin as first-line therapy for recurrent or metastatic head and neck cancer: A single-arm, multicenter, phase 2 trial

OBJECTIVES

Macropinocytosis promotes internalization of albumin into cells to serve as a nutrient supply and is constitutively driven by signaling pathways frequently hyperactivated in head and neck squamous-cell carcinoma (HNSCC). In this way, drugs bound to albumin may selectively target HNSCC. nab-paclitaxel is a nanoparticle albumin-bound formulation of paclitaxel that improves drug delivery into tumor compared to paclitaxel. The primary aim of this single-arm, multicenter, phase 2 trial was to determine if nab-paclitaxel, cetuximab, and carboplatin (CACTUX regimen) would result in longer progression-free survival (PFS) than the historical regimen (EXTREME: 5-fluorouracil, cetuximab, and a platinum).

MATERIALS AND METHODS

Patients with untreated recurrent or metastatic HNSCC received six, three-week cycles of nab-paclitaxel, cetuximab, and carboplatin, followed by maintenance nab-paclitaxel and cetuximab until progression. We hypothesized the median PFS with CACTUX would be 35% longer than with EXTREME (corresponding to 7.6 vs 5.6 months; power 0.80, α = 0.05, one-sided test, n = 70). Secondary outcomes included objective response rate (ORR) and overall survival (OS).

RESULTS

Seventy-four patients enrolled into the trial; seventy were evaluable. The median PFS was 6.1 months (95% CI, 4.1-7.4). The ORR was 60%. Median follow-up was 18 months (IQR: 4.7-23). The median OS was 17.8 months (95% CI, 8.5-21.7) for all patients, and 19.8 months (95% CI, 10.9-22.0) for human papillomavirus (HPV)-related oropharynx SCC and 14.0 months (95% CI, 4.6-23.3) for HPV-unrelated HNSCC.

CONCLUSION

Among patients with recurrent or metastatic HNSCC, CACTUX did not result in a longer PFS than historical EXTREME. However, CACTUX did result in a more favorable ORR and OS.

FOLFIRINOX for the Treatment of Advanced Gastroesophageal Cancers: A Phase 2 Nonrandomized Clinical Trial

Importance

Standard first-line regimens for patients with metastatic gastroesophageal adenocarcinomas have an approximate 40% objective response rate (ORR). The combination of leucovorin, fluorouracil, irinotecan, and oxaliplatin (FOLFIRINOX) has been efficacious as first-line therapy for other gastrointestinal cancers, such as pancreatic and colon cancers.

Objective

To evaluate the clinical activity and safety of FOLFIRINOX as first-line treatment for patients with advanced gastroesophageal adenocarcinoma.

Design, Setting, and Participants

This is an open-label, single-arm phase 2 study of first-line FOLFIRINOX in patients with advanced gastroesophageal adenocarcinoma. Estimated sample size included 41 patients with ERBB2-negative disease with 90% power to detect an ORR of 60% or greater with α of .10. No enrollment goal was planned for ERBB2-positive patients, but they were allowed to receive trastuzumab in combination with FOLFIRINOX.

Interventions

Starting doses were fluorouracil, 400 mg/m2 bolus, followed by 2400 mg/m2 over 46 hours; leucovorin, 400 mg/m2; irinotecan, 180 mg/m2; and oxaliplatin, 85 mg/m2. Trastuzumab was administered as a 6 mg/kg loading dose, followed by 4 mg/kg every 14 days in patients with ERBB2-positive disease.

Main Outcomes and Measures

The primary end point was ORR by the Response Evaluation Criteria in Solid Tumors, version 1.1. Secondary end points included safety profile, progression-free survival (PFS), overall survival (OS), and duration of response.

Results

From November 2013 to May 2018, 67 patients were enrolled (median [range] age, 59.0 [34-78] years; including 56 [84%] men), and 26 of 67 (39%) had ERBB2-positive disease. Median follow-up was 17.4 months. The ORR was 61%(95% CI, 44.5%-75.8%) (25 of 41) in the ERBB2-negative group and 85% (95% CI, 65.1%-95.6%) (22 of 26) in the ERBB2-positive group, including 1 patient with complete response. For ERBB2-negative patients, median PFS was 8.4 months and median OS was 15.5 months; for ERBB2-positive patients, median PFS was 13.8 months and median OS was 19.6 months. Fifty-six patients (84%) had dose modifications or treatment delays. The most common toxic effects were neutropenia (91%, n = 61), diarrhea (63%, n = 42), peripheral sensory neuropathy (61%, n = 41), and nausea (48%, n = 32), with no unexpected toxic effects.

Conclusions and Relevance

The FOLFIRINOX regimen with or without trastuzumab was associated with improved ORR and PFS in patients with advanced gastroesophageal adenocarcinoma in the first-line setting. This regimen may be a reasonable therapeutic option for patients with preserved performance status.

Trial Registration

ClinicalTrials.gov Identifier: NCT01928290.

Mutation profile differences in younger and older patients with advanced breast cancer using circulating tumor DNA (ctDNA)

PURPOSE

Little is known regarding the mutation profiles of ctDNA in the older adult breast cancer population. The objective of this study is to assess differences in mutation profiles in the older adult breast cancer population using a ctDNA assay as well as assess utilization of testing results.

METHODS

Patients with advanced breast cancer underwent molecular profiling using a plasma-based ctDNA NGS assay (Guardant360) between 5/2015 and 10/2019 at Siteman Cancer Center. The profiling results of a multi-institutional database of patients with advanced breast cancer who had undergone molecular profiling were obtained. Associations between mutations and age group (≥ 65 vs. < 65) were examined using a Fisher's exact test.

RESULTS

In the single-institutional cohort, 148 patients (69.2%) were < 65 years old and 66 patients (30.8%) ≥ 65 years old. ATM, BRAF, and PIK3CA mutations were found more frequently in older patients with ER + HER2- breast cancers (p < 0.01). In the multi-institutional cohort, 5367 (61.1%) were < 65 years old and 3417 (38.9%) ≥ 65 years old. ATM, PIK3CA, and TP53 mutations were more common in the older cohort (p < 0.0001) and MYC and GATA3 mutations were less common in the older cohort (p < 0.0001). CtDNA testing influenced next-line treatment management in 40 (19.8%) patients in the single-institutional cohort.

CONCLUSION

When controlling for subtype, results from a single institution were similar to the multi-institutional cohort showing that ATM and PIK3CA were more common in older adults. These data suggest there may be additional molecular differences in older adults with advanced breast cancers.

Abstract P1-19-13: A phase II trial assessing the safety of an alternative dosing schedule of palbociclib (palbo) in hormone receptor positive (HR+), HER2 negative (HER2-) metastatic breast cancer (MBC): Alt Dose Palbo

Introduction: Palbo is approved in combination with an aromatase inhibitor or fulvestrant (FUL) for the treatment of HR+ HER2- MBC. The incidence of grade (G) 3/4 neutropenia (ANC) approaching 66% has been observed in phase 3 trials of palbo. We hypothesize that an alternative schedule of palbo, 5 days on/2 days off every 7 days, reduces the severity of neutropenia, therefore allowing continued weekly dosing and less dose reduction and discontinuation. Methods: A single arm phase II study (Alt Dose Palbo) was conducted in patients (pts) with HR+ HER2- MBC who had ≤1 prior systemic therapy in the metastatic setting (NCT03007979). Pts were treated with palbo 125 mg daily on a 5 days on/2 days off every 7-day schedule, along with letrozole (LET) or FUL per treating physician. Goserelin was administered if premenopausal. The primary objective was to determine the rate of G3/4 ANC within the first 29 days of treatment. Secondary objectives included determining the rate of G3/4 ANC during all cycles, rate of palbo dose reduction/interruption/discontinuation, adverse event (AE) profile per CTCAE v5, progression free survival (PFS), objective response rate (ORR) and clinical benefit rate (CBR) by RECIST 1.1. The sample size of 47 was calculated to provide 90% power based on one-sample binomial exact test at a 5% alpha level to test the one-sided null hypothesis of G3/4 ANC rate &gt;62% versus the alternative of &lt;40%. If G3/4 ANC was not observed in 24 or more pts, this alternative dosing will be deemed to have a better toxicity profile than standard schedule. Results: Between July 2017 to June 2019, 48 pts were enrolled at 2 institutions. 3 pts withdrew/went off during cycle 1 unrelated to the study, leaving 45 pts (33 LET, 12 FUL) with a median age of 63 (range: 34-87) years and visceral metastases in 23 (51%). Prior (neo) adjuvant chemotherapy and endocrine therapy (ET) were received in 20 (44%) and 25 (56%) pts, respectively. Six (13%) had 1 prior ET in the metastatic setting. 19 (42%) had primary or secondary endocrine resistance defined according to the ESMO advanced breast cancer guideline prior to enrollment to the study. As of July 1, 2019, with a median follow up of 9.5 months, 28 (62%) pts are still receiving study drug. 42 pts were evaluable for toxicities. There were no G4 AEs. Nine (21%) and 15 (36%) pts experienced G3 ANC in cycle 1 (up to day 29), and all cycles, respectively. 33 pts in cycle 1 and 27 pts in all cycles, did not experience G3/4 ANC during all cycles, exceeding the predefined boundary for better tolerability of this schedule. Palbo was dose reduced in 10 (23.8%) pts. Two (4.8%) discontinued palbo due to AE (one with G3 ANC not recovering to G1 in 2 wks and the other died (G5 event) with acute subdural hematoma with concurrent G3 thrombocytopenia). The common treatment related AEs are shown in the Table 1. The ORR was 48% (2 CR, 10 PR, 95% Wilson CI: 30-66.5%) among 25 evaluable pts. The CBR (defined by CR or PR or stable disease for at least 24 wks) was 76.74% (33 of 43 evaluable pts, 95% Wilson CI: 62.3-86.9%). PFS has not been evaluated. Conclusion: The Alt Dose Palbo trial with palbo scheduled at 5 days on/2 days off every 7 days, with no weeks off therapy, met its primary endpoint with reduced G3/4 ANC. Survival data is not yet mature and will be updated at the presentation. However, preliminary efficacy data appears comparable to prior report. Encouraging data from this study should be confirmed in a randomized study.

Table 1C1 D1-29 AEG1G2G3TotalWBC decreased26%50%17%93%ANC decreased10%43%21%74%Anemia38%12%0%50%Fatigue29%0%0%29%Platelets decreased14%0%2%17%Nausea12%2%0%14%All cycle AEG1G2G3TotalWBC decreased19%50%26%95%ANC decreased5%40%36%81%Anemia50%21%2%74%Fatigue36%5%0%40%Nausea26%2%0%29%Platelets decreased24%0%2%26%Alopecia21%0%0%21%Mucositis19%0%0%19%Hot flashes17%2%0%19%Constipation14%0%0%14%Arthralgia12%2%0%14%AST elevated10%0%2%12%Anorexia12%0%0%12%ALT elevated7%0%5%12%

Citation Format: Jairam Krishnamurthy, Jingqin Luo, Foluso Ademuyiwa, Rama Suresh, Caron Rigden, Timothy Reardon, Katherine Weilbaecher, Ashley Frith, Anna Roshal, Pavan Tandra, Mathew Cherian, Tracy Summa, Shana Thomas, Leonel Hernandez-Aya, Lindsay Peterson, Cynthia Ma. A phase II trial assessing the safety of an alternative dosing schedule of palbociclib (palbo) in hormone receptor positive (HR+), HER2 negative (HER2-) metastatic breast cancer (MBC): Alt Dose Palbo [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-19-13.

Randomized controlled trial of high-dose versus standard-dose vitamin D3 for prevention of aromatase inhibitor-induced arthralgia

PURPOSE

Half of hormone receptor-positive (HR+) breast cancer patients will develop joint pain, termed aromatase inhibitor-induced arthralgia (AIA), while taking aromatase inhibitor therapy. Though there is no universally accepted effective treatment for AIA, there has been some evidence to support high-dose vitamin D as a treatment.

METHODS

We randomized post-menopausal women who were beginning adjuvant AI therapy to receive standard-dose vitamin D3 (800 IU daily for 52 weeks), or high-dose vitamin D3 (50,000 IU weekly for 12 weeks, followed by 2000 IU daily for 40 weeks). The primary end point was development of AIA. The trial was designed to enroll 184 patients. This futility analysis was performed after 93 patients were enrolled.

RESULTS

The high-dose vitamin D regimen was effective in raising serum vitamin D levels, but there was no significant difference in development of AIA between the two arms. In the high-dose arm, 25 patients (54%) developed AIA, compared to 27 patients (57%) in the standard-dose arm. The planned futility analysis was positive; thus, the study was terminated. Neither baseline vitamin D nor 12-week vitamin D level was predictive of AIA development.

CONCLUSION

Although vitamin D levels were increased in the high-dose arm, there was no significant signal for benefit of high-dose vitamin D supplementation for AIA prevention in this unblinded trial. This study, along with several others, implies that vitamin D likely does not play a significant role in AIA for the majority of patients.

Abstract PD6-02: A randomized, controlled trial of high dose vs. standard dose vitamin D for aromatase inhibitor-induced arthralgia in breast cancer survivors

Background: Approximately half of women on aromatase inihbitor (AI) therapy develop AI-induced arthralgia (AIA), and many discontinue the medication because of this common side effect. While Vitamin D has been studied as a treatment for AIA, trial results have been conflicting thus far.

Patients and Methods: All subjects were post menopausal women who were beginning adjuvant AI therapy for stage I-III hormone receptor positive breast cancer. Patients were randomized 1:1 to receive standard dose vitamin D3 (800 IU daily for 52 weeks) or high dose vitamin D3 (50,000 IU weekly for 12 weeks, followed by 2000 IU daily for 40 weeks). All patients also took oral calcium 600 mg daily. The primary endpoint was development of AIA, as defined by pre-specified changes in the Health Assessment Questionnaire II (HAQ-II). Secondary endpoints include compliance with AI therapy, and correlation between grip strength and development of AIA. Exploratory endpoint was measurement of inflammatory cytokine reduction in each arm. The trial was designed to enroll 184 patients, but this futility analysis was performed after 93 patients were enrolled. The futility boundary for stopping the trial early was calculated as p = 0.47.

Results: All 93 patients (46 in the high dose arm, and 47 in the standard dose arm) enrolled in the study at the time of the interim analysis were evaluable. The HAQ-II was completed at 12 weeks in 76% on the high dose arm, and 68% in the standard dose arm. Subjects who did not complete the questionnaire were deemed as study failures (i.e. development of AIA was assumed). In the high dose arm, 25 patients (54%) developed AIA, compared to 27 patients (57%) in the standard dose arm. The one-tailed p value is 0.3818, and the Z-score is 0.3, yielding only a 38% conditional power that that study would find a significant difference between the two arms. Thus, the study was terminated early for futility. There was no significant difference between the two arms in adherence to AI therapy. The grip strength and inflammatory cytokine data are pending at this time. They will be ready by the time of the conference.

Conclusions: There was no significant signal for benefit of high dose vitamin D supplementation, as compared to standard dose vitamin D, for AIA prevention in post menopausal women taking adjuvant AI therapy. These results further characterize the role of Vitamin D in AIA, and they inform future clinical trials in this arena. Further research is necessary, as this remains an important cause of non-adherence to this highly effective therapy.

Citation Format: Niravath P, Wang T, Hilsenbeck SG, Lipscomb K, Pavlick A, Jiralerspong S, Nangia J, Ellis M, Ademuyiwa F, Cherian M, Frith A, Ma C, Park H, Rigden C, Suresh R, Osborne CK, Rimawi MF. A randomized, controlled trial of high dose vs. standard dose vitamin D for aromatase inhibitor-induced arthralgia in breast cancer survivors [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD6-02.

A Phase I Trial of Temsirolimus and Pemetrexed in Patients with Advanced Non-Small Cell Lung Cancer

BACKGROUND

Pemetrexed is an antifolate chemotherapeutic agent approved for use in non-small cell lung cancer (NSCLC). The mammalian target of rapamycin (mTOR) pathway is implicated in lung cancer development and inhibited by temsirolimus.

METHODS

We performed a phase I study evaluating the combination of pemetrexed and temsirolimus in advanced non-squamous NSCLC.

RESULTS

Eight patients were enrolled in this study. The dose-limiting toxicities included grade 4 thrombocytopenia, grade 3 leukopenia and grade 3 neutropenia. The maximum tolerated dose was determined to be pemetrexed 375 mg/m2 intravenously on day 1 and temsirolimus 25 mg intravenously on days 1, 8 and 15. No objective responses were noted and 3 patients had stable disease as the best response.

CONCLUSION

The combination of pemetrexed and temsirolimus is feasible and well tolerated. This combination may be further evaluated in patients with mTOR pathway activation, particularly in those with TSC1 or STK11 mutations.

Five fractions of radiation therapy followed by 4 cycles of FOLFOX chemotherapy as preoperative treatment for rectal cancer

BACKGROUND

Preoperative radiation therapy with 5-fluorouracil chemotherapy is a standard of care for cT3-4 rectal cancer. Studies incorporating additional cytotoxic agents demonstrate increased morbidity with little benefit. We evaluate a template that: (1) includes the benefits of preoperative radiation therapy on local response/control; (2) provides preoperative multidrug chemotherapy; and (3) avoids the morbidity of concurrent radiation therapy and multidrug chemotherapy.

METHODS AND MATERIALS

Patients with cT3-4, any N, any M rectal cancer were eligible. Patients were confirmed to be candidates for pelvic surgery, provided response was sufficient. Preoperative treatment was 5 fractions radiation therapy (25 Gy to involved mesorectum, 20 Gy to elective nodes), followed by 4 cycles of FOLFOX [5-fluorouracil, oxaliplatin, leucovorin]. Extirpative surgery was performed 4 to 9 weeks after preoperative chemotherapy. Postoperative chemotherapy was at the discretion of the medical oncologist. The principal objectives were to achieve T stage downstaging (ypT < cT) and preoperative grade 3+ gastrointestinal morbidity equal to or better than that of historical controls.

RESULTS

76 evaluable cases included 7 cT4 and 69 cT3; 59 (78%) cN+, and 7 cM1. Grade 3 preoperative GI morbidity occurred in 7 cases (9%) (no grade 4 or 5). Sphincter-preserving surgery was performed on 57 (75%) patients. At surgery, 53 patients (70%) had ypT0-2 residual disease, including 21 (28%) ypT0 and 19 (25%) ypT0N0 (complete response); 24 (32%) were ypN+. At 30 months, local control for all evaluable cases and freedom from disease for M0 evaluable cases were, respectively, 95% (95% confidence interval [CI]: 89%-100%) and 87% (95% CI: 76%-98%). Cases were subanalyzed by whether disease met requirements for the recently activated PROSPECT trial for intermediate-risk rectal cancer. Thirty-eight patients met PROSPECT eligibility and achieved 16 ypT0 (42%), 15 ypT0N0 (39%), and 33 ypT0-2 (87%).

CONCLUSION

This regimen achieved response and morbidity rates that compare favorably with those of conventionally fractionated radiation therapy and concurrent chemotherapy.

A single-institution phase II trial of five fractions of radiotherapy followed by four courses of FOLFOX chemotherapy as preoperative therapy for rectal adenocarcinoma

553

Background: Preoperative radiotherapy (RT) with 5FU chemotherapy (CT) is a standard of care for cT3-4 rectal cancer. Studies incorporating additional cytotoxic agents have resulted in increased morbidity with little benefit. We evaluate a template that seeks to (1) include the known benefits of preoperative RT on local response/control, (2) provide for preoperative multi-drug CT, (3) avoid the morbidity of concurrent RT and multi-drug CT.

Methods: Patients with cT3-4, any N, any M rectal cancer were eligible. Patients were confirmed to be candidates for surgery, provided the response was sufficient. Preoperative treatment was 5 fractions RT (25 Gy to involved mesorectum, 20 Gy to elective nodes), followed by 4 cycles of mFOLFOX6. Postoperative CT was at the discretion of the medical oncologist. The principal objectives are to demonstrate that this regimen can achieve T stage down staging (ypT < cT) and acute grade 3+ gastrointestinal (GI) morbidity equal to or better than historical controls.

Results: Accrual opened late 2009, with 60 patients enrolled through 8/2011. Forty-six have had sufficient time to proceed to surgery with 4 having grade 3 preoperative GI morbidity. Two cases are inevaluable for response: one withdrew consent prior to CT and one received no surgery due to progression of cM1 disease (with local response). The 44 evaluable cases included 4 cT4 and 40 cT3; 32 (73%) cN+, 4 cM1. At surgery 33 (75%) had ypT0-2 residual disease including 13 (30%) ypT0, 14 (32%) were ypN+. Cases were sub-analyzed by whether disease was too advanced for the upcoming ACOSOG preoperative FOLFOX vs. 5FU-RT trial. By ACOSOG eligibility, response rates were (eligible first, ineligible second) ypT0: 10/22 (45%) vs. 3/22 (14%) (p = 0.05), ypT0-2: 19/22 (86%) vs. 14/22 (64%) (p = NS).

Conclusions: This regimen achieves high response rates with acceptable morbidity. The response for ACOSOG eligible cases meets pre-determined stopping criteria for proceeding to a randomized trial. Our successor study will randomize to this regimen vs. FOLFOX alone for ACOSOG eligible cases, while initially continuing as a single arm trial for ACOSOG ineligible cases.