Phase II Study of Afatinib in Patients With Tumors With Human Epidermal Growth Factor Receptor 2–Activating Mutations: Results From the National Cancer Institute–Molecular Analysis for Therapy Choice ECOG-ACRIN Trial (EAY131) Subprotocol EAY131-B

PURPOSE

National Cancer Institute–Molecular Analysis for Therapy Choice is a multicohort trial that assigns patients with advanced cancers to targeted therapies on the basis of central tumor genomic testing. Arm B evaluated afatinib, an ErbB family tyrosine kinase inhibitor, in patients with ERBB2-activating mutations.

METHODS

Eligible patients had selected ERBB2 single-nucleotide variants or insertions/deletions detected by the National Cancer Institute–Molecular Analysis for Therapy Choice next-generation sequencing assay. Patients had performance status ≤ 1, left ventricular ejection fraction > 50%, grade ≤ 1 diarrhea, and no prior human epidermal growth factor receptor 2 (HER2) therapy. Patients received afatinib 40 mg once daily in 28-day cycles. The primary end point was objective response rate (ORR). Secondary end points were 6-month progression-free survival, overall survival, toxicity, and molecular correlates.

RESULTS

A total of 59 patients were assigned and 40 were enrolled. The median age was 62 years, 78% were female, 68% had performance status = 1, and 58% had received > 3 prior therapies. The confirmed ORR was 2.7% (n = 1 of 37; 90% CI, 0.14 to 12.2), and 6-month progression-free survival was 12.0% (90% CI, 5.6 to 25.8). A confirmed partial response occurred in a patient with adenocarcinoma of extra-mammary Paget disease of skin who progressed after cycle 6. Two unconfirmed partial responses were observed (low-grade serous gynecological tract and estrogen receptor–positive/HER2-negative immunohistochemistry breast ductal carcinoma). Of 12 patients with breast cancer, 1 additional patient with lobular carcinoma (estrogen receptor–positive/HER2 fluorescent in situ hybridization) had a 51% reduction in target lesions but progressed because of a new lesion at cycle 6. The most common (> 20%) treatment-related adverse events were diarrhea (68%), mucositis (43%), fatigue (40%), acneiform rash (30%), dehydration (27%), vomiting (27%), nausea (27%), anemia (27%), and anorexia (22%). Four patients (11%) discontinued because of adverse events.

CONCLUSION

Although afatinib did not meet the prespecified threshold for antitumor activity in this heavily pretreated cohort, the response in a rare tumor type is notable. The safety profile of afatinib was consistent with prior studies.

INTRODUCTION

The human epidermal growth factor receptor (HER) family pathway includes four members, HER1 (epidermal growth factor receptor or ErbB1), HER2 (ErbB2), HER3 (ErbB3), and HER4 (ErbB4), that regulate critical oncogenic cellular functions. HER2 overexpression and/or amplification (also known as HER2+) is a poor prognostic marker in breast and gastric or gastroesophageal junction cancers.^1,2 HER2-targeted antibodies,^3-5 antibody-drug conjugates,^6,7 and small-molecule inhibitors^8-10 are approved for the treatment of HER2+ breast and gastric cancers on the basis of improvement in survival outcomes.

CONTEXT

• Key Objective

• National Cancer Institute–Molecular Analysis for Therapy Choice is a multicohort trial that assigns patients with refractory cancers to targeted therapies on the basis of DNA mutation testing. The primary objective of arm B was to evaluate the objective response rate (ORR) by RECIST v1.1 of afatinib, an oral ErbB family tyrosine kinase inhibitor, in patients with selected ERBB2 (human epidermal growth factor receptor 2)-activating mutations.

• Knowledge Generated

• A confirmed partial response was observed in a patient with extra-mammary Paget disease of the skin, for a confirmed ORR of 2.7% (n = 1 of 37; 90% CI, 0.14 to 12.2). The 6-month progression-free survival rate was 12.7% (90% CI, 5.6 to 25.8). Comutation of TP53 was associated with progression as best response to afatinib (P = .015).

• Relevance

• Afatinib did not meet the prespecified threshold for antitumor activity in ERBB2-mutated advanced solid tumors. The response observed in a patient with extra-mammary Paget disease, a rare tumor type with no standard therapy, is notable and warrants further investigation.

Somatic mutations in the kinase, transmembrane, or extracellular domain of HER2 in the absence of ERBB2 amplification are observed in < 5% across a variety of solid tumors,^11,12 including breast, non–small-cell lung (NSCLC), bladder, cervical, colorectal, and ovarian cancers. Variants in HER2 are distributed at multiple loci across the HER2 gene, which varies according to tumor type. Preclinical studies demonstrate that selected HER2 variants activate HER2 intracellular signaling^13,14 or enhance noncovalent HER2/HER3 receptor heterodimerization¹⁵ that can be pharmacologically inhibited by HER2-targeted therapies.

Afatinib is a potent, orally bioavailable small molecule HER2 family irreversible inhibitor that is approved for the treatment of patients with metastatic NSCLC whose tumors have epidermal growth factor receptor exon 19 deletions or exon 21 (L858R) substitution mutations and for metastatic squamous NSCLC progressing after platinum-based chemotherapy. In cervical cancer cells with activating HER2 extracellular domain mutations (S280F and E375D), afatinib reduced intracellular HER2 signaling and led to cell cycle arrest in the G1 phase.¹⁶ Similarly, antitumor activity has been observed in patients with metastatic NSCLC with HER2 mutations treated with afatinib.^17-20

The National Cancer Institute–Molecular Analysis for Therapy Choice (NCI-MATCH) trial is a national, multicohort, histology agnostic, signal-finding trial that assigns patients with refractory cancers to targeted therapies on the basis of central tumor genomic testing.²¹ The primary objective of subprotocol B of NCI-MATCH was to evaluate the objective response rate (ORR) for patients with HER2 mutations (other than NSCLC) treated with afatinib. Secondary objectives were to evaluate 6-month progression-free survival, overall survival (OS), toxicity, and molecular correlates.

METHODS

Patient Eligibility

Patients with refractory solid tumors, lymphoma, or multiple myeloma whose disease had progressed after at least one line of standard systemic therapy, or for whom no standard therapy was available, were eligible for NCI-MATCH. Informed consent was obtained from each participant or each participant's guardian before enrollment. To be assigned to this subprotocol, patients had tumor biopsies with selected ERBB2 single-nucleotide variants (SNVs) or insertions/deletions (indels; Appendix Table A1, online only), with no evidence of ERBB2 gene amplification, detected through centralized testing with the NCI-MATCH next-generation sequencing (NGS) assay, which included 143 genes (customized Thermo Fisher Oncomine AmpliSeq)^22-24 or detected by testing in a Clinical Laboratory Improvement Amendments–certified laboratory participating in NCI-MATCH. Key eligibility requirements included Eastern Cooperative Oncology Group performance status 0-1, measureable disease by RECIST version 1.1, left ventricular ejection fraction > 50% with no clinically relevant electrocardiogram abnormalities, and adequate bone marrow, renal, and hepatic function. Patients with NSCLC, prior HER2-targeted therapy, a history of interstitial lung disease, or diarrhea grade > 1 as per Common Terminology Criteria for Adverse Events (CTCAE) version 4.0 at baseline were excluded. The study was approved by the NCI Central Institutional Review Board (ClinicalTrials.gov identifier: NCT02465060).

Treatment and Evaluation

Eligible patients were treated with afatinib 40 mg oral once daily dosing in 28-day cycles until RECIST progression or unacceptable toxicity. Concomitant endocrine therapy was not allowed for patients with estrogen receptor–positive (ER+) breast cancers. Patients did not receive prophylactic antidiarrheal therapy. Treatment response was evaluated by CT or MRI every two cycles using RECIST v1.1.²⁵ Patients were assessed weekly for the first 3 weeks and then at the beginning of each treatment cycle for adverse events (AEs) using CTCAE version 4.0. Left ventricular fraction was assessed by echocardiogram or nuclear scan every two cycles.

Statistical Design

The primary end point was objective response rate, with response defined as a complete or partial response (PR) by RECIST version 1.1. Allowing for 10% response inevaluability, initial planned enrollment was 35 patients with response in ≥ 5 of 31 (16%) required to consider the agent promising and warranting further study. This initial sample size provided 92% power to detect an improvement from 5% under the null hypothesis to 25% with afatinib treatment, with a one-sided type 1 error of 1.8%. Accrual continued past 35 patients on the basis of protocol criteria allowing up to 6 months of additional accrual and a maximum of 35 additional patients. A subsequent protocol amendment permitted accrual of up to 70 patients. Secondary end points included 6-month progression-free survival, OS, toxicity, and molecular coalterations associated with treatment response.

RESULTS

Patient Characteristics

There were 59 patients with a qualifying ERBB2 actionable mutation on NCI-MATCH tumor NGS testing assigned to this subprotocol (Fig 1). Of these patients, 40 were enrolled between October 5, 2015, and June 20, 2017. One patient was ineligible (creatinine clearance out of normal range), and 2 patients were eligible but did not receive afatinib treatment; therefore, 37 were included in efficacy analysis. Patient characteristics are provided in Table 1: The median age was 62 years, 78% were female, 68% had Eastern Cooperative Oncology Group performance status 1, and 58% had received > 3 prior systemic therapies. The most common tumor types were ER+ breast (33%), colorectal (14%), urothelial (11%), biliary (8%), cervical (5%) and small bowel (5%) cancers. Of the 12 patients with metastatic breast cancer enrolled to this subprotocol, all had ER+ disease and 5 (42%) had invasive lobular carcinoma (ILC). There were 44 qualifying ERBB2 variants (Fig 2): 30 patients had 1 qualifying ERBB2 SNV, 2 patients had 2 qualifying ERBB2 SNVs, 5 patients had 1 qualifying ERBB2 indel, 2 patients had 1 ERBB2 SNV and 1 ERBB2 indel, and 1 patient had ERBB2 SNV and copy number variant. The most common qualifying ERBB2 variants were known mutation hotspots, including S310F (n = 7), L755S (n = 7), V777L (n = 6), V842I (n = 6), D769Y (n = 4), S310Y (n = 4), V777_G778insGSP (n = 3), E770_A771insAYVM (n = 3), and others (n = 3).

FIG 1.

CONSORT diagram.

TABLE 1.

Patient Characteristics

FIG 2.

ERBB2 variants of patient enrolled according to gene position. The number in parenthesis indicated the number of variants detected.

Efficacy

As of the data lock for efficacy analysis on January 22, 2021, the ORR was 2.7% (n = 1 of 37; 90% CI, 0.14 to 12.2). In addition, 14 patients had stable disease as best response (37.8%), and 19 patients had progression as best response (54.1%). There were three patients who were not evaluable for response because of baseline scan being out of window, first follow-up evaluation being too long from enrollment, and death before the first radiological response assessment. The only confirmed RECIST response was observed in a patient with extra-mammary Paget disease (EMPD) of the skin (ERBB2 D769Y mutation) who progressed after cycle 6. Two additional RECIST responses were observed in one patient with primary peritoneal carcinoma (ERBB2 D769Y mutation) and one with ER+ invasive ductal breast cancer (ERBB2 V777L mutation) that were not confirmed on follow-up radiological assessments. An additional patient with ER+ lobular breast cancer (ERBB2 S310F mutation) had a best reduction of RECIST target lesions of 51% after six cycles but progressed because of a new nontarget lesion (Fig 3A).

FIG 3.

(A) Waterfall plot of best change from baseline for 28 patients with follow-up target lesion measurements by RECIST v1.1. Color shows histology. For the 9 patients not shown: unevaluable (n = 3) for RECIST and progression because of new lesion (n = 6) without target lesion measurements. (B) Treatment duration in patients who achieved stable disease or PR (N = 15). Color shows histology. (C) Kaplan-Meier curve with 90% CI for PFS. (D) Kaplan-Meier curve with 90% CI for OS. ER+, estrogen receptor–positive; OS, overall survival; PD, progressive disease; PFS, progression-free survival; PR, partial response; SD, stable disease.

The 6-month progression-free survival (PFS) rate was 12.0% (90% CI, 5.6 to 25.8). At the time of database lock, there were five patients who achieved PR or stable disease for ≥ 6 cycles (Fig 3B): ovarian endometrioid adenocarcinoma (ERBB2 D769Y, treatment discontinued after nine cycles for surgery), colorectal cancer (ERBB2 V777L and D769Y comutations; treatment discontinued after eight cycles for symptomatic deterioration), EMPD of skin (ERBB2 D769Y mutation, treatment discontinued after six cycles for progression), cervical cancer (ERBB2 S310F mutation, treatment discontinued after six cycles for progression), and plexiform neurofibroma of the parotid gland (ERBB2 V777L mutation, treatment discontinued after one cycle for AE without progression reported 20 months after enrollment). Thirty-two of the 37 patients experienced a PFS event, and the median PFS was 1.7 months (90% CI, 1.6 to 4.2; Fig 3C). Thirty-four patients died, and the median OS was 6.5 months (90% CI, 4.9 to 8.9; Fig 3D).

Safety

The median number of cycles of afatinib administered was two (range, 1-9). A total of 14 patients (38%) had at least one incidence of dose modification while on treatment, including four patients (11%) who discontinued because of an AE. Thirty-seven patients were included in the toxicity analysis (excluding two who did not receive afatinib treatment and one who was not assessed for toxicity). The most common all-grade treatment-related AEs (> 20%) were diarrhea (68%), mucositis (43%), fatigue (40%), acneiform rash (30%), dehydration (27%), vomiting (27%), nausea (27%), anemia (27%), and anorexia (22%; Table 2). The most frequent grade 3 treatment-related AEs were diarrhea (18.9%), mucositis (8.1%), and fatigue (8.1%). There were 82 serious AEs reported from 22 unique patients. There were no treatment-related deaths.

TABLE 2.

Treatment-Related AEs in Patients Who Received Treatment With Afatinib and Had Toxicity Assessed (N = 37)

Correlative Studies

To identify potential mechanisms that may have contributed to the low ORR, we performed secondary analysis of co-occurring alterations. Immunostaining for PTEN was intact in 33 of 34 (97%) of patients. TP53 (38%) and PIK3CA (22%) were the most frequently identified co-occurring mutations (Fig 4). There was a positive association between progression as best response to afatinib and co-occurrence of TP53 (Fisher's exact test P = .015) but not PIK3CA comutations.

FIG 4.

Oncoprint showing identified variant types in ERRB2, co-occuring mutations, histology, and best overall response. CNV, copy number variant; indel, insertion or deletion; SNV, single-nucleotide variant.

DISCUSSION

In this subprotocol of the NCI-MATCH trial, afatinib did not meet the prespecific threshold for promising antitumor activity, with an ORR of 2.7% in patients with ERBB2-mutated advanced solid tumors. The response observed in a rare tumor type, EMPD, is notable. EMPD is an aggressive cutaneous adenocarcinoma that usually arises in the anogenital area and axillae outside the mammary glands with no established standard treatment for metastatic disease. ERBB2 gene amplification and/or HER2 protein overexpression is observed in 15%-58% of EMPD, with case reports of antitumor activity observed with taxane chemotherapy in combination with the HER2 monoclonal antibody trastuzumab.²⁶ A patient-derived xenograft murine model of EMPD with ERBB2 S310F mutation was sensitive to HER2 pathway inhibition with combined trastuzumab and lapatinib therapy.²⁷ Our findings support the rationale for HER2 blockade in EMPD with an ERBB2 mutation.

In our study, clinical activity was also observed in patients with ER+ breast (unconfirmed PR and 51% reduction of target lesions with appearance of a new metastasis) as well as gynecological malignancies (unconfirmed PR in primary peritoneal carcinoma and two patients with SD > 6 months with ovarian endometrioid and cervical cancers). This differential activity on the basis of tumor histology is consistent with the SUMMIT basket trial of the HER2 kinase inhibitor neratinib in patients with ERBB2-mutant solid tumors, with the highest response rates observed in breast, cervical, and biliary cancers.^12,28 Cross-trial comparisons of the results of our trial versus the SUMMIT trial should be interpreted with caution as there are differences in the primary end point for antitumor activity between the two trials: confirmed RECIST ORR in our trial versus ORR (unconfirmed) at 8 weeks in the SUMMIT trial.¹² There were also differences in eligibility criteria as all patients in the NCI-MATCH trial were enrolled on the basis of central NGS testing results from contemporaneous metastatic tumor biopsies identifying qualifying ERBB2 mutations before enrollment versus the SUMMIT trial that allowed local testing of tissue- (including archival tumor tissue) or plasma-based sequencing assays.

ERBB2-mutant solid tumors treated with HER2 kinase inhibitors can develop acquired resistance through the emergence of gatekeeper and/or gain-of-function ERBB2^29,30 mutations, including polyclonal ERBB2 resistance mutations identified within the same patient through circulating tumor DNA. In our trial, we did not assess mechanisms of acquired resistance to afatinib. However, the only patient with a confirmed PR progressed after cycle 6, and two additional patients with unconfirmed PR progressed at their next restaging CT scan, supporting the paradigm that there are convergent mechanisms of acquired resistance to HER2 kinase inhibition that rapidly develop in ERBB2-mutant solid tumors.

It is noteworthy that all 12 patients with breast cancer having ERBB2 mutation(s) enrolled in our study were ER+, confirmed by central testing with ER immunohistochemistry. ERBB2 mutations are found in up to 4% of all breast cancers¹¹ and are more frequently identified in ER+ breast cancers including ILC³¹ and, particularly, pleomorphic³² and solid³³ histological subtypes of ILC. Nonrandomized cohorts of patients with ER+ breast cancer having ERBB2 mutation(s) treated with neratinib in combination with the selective ER degrader fulvestrant compared with neratinib monotherapy from the SUMMIT trial reported a higher response rate (29.8% v 17.4%), duration of response (9.0 v 7.4 months), and clinical benefit rate (46.8% v 30.4%) for combination therapy.³⁴ The addition of trastuzumab, to more potently inhibit intracellular HER2 signaling, to neratinib and fulvestrant in the SUMMIT trial led to a higher observed response rate (45.9%), duration of response (10.9 months), and clinical benefit rate (54.9%).³⁵ The clinical utility of adding a HER2 kinase inhibitor to ER-targeted therapy remains uncertain; a retrospective case-control study from the AACR Project GENIE reported similar time to progression on first-line endocrine therapy and OS for ER+, ERBB2-mutant cancer compared with matched ER+, ERBB2 wild-type controls.³⁶ The SUMMIT trial has been amended to include 1:1:1 random assignment for ER+, ERBB2-mutant breast cancers to fulvestrant alone, fulvestrant combined with trastuzumab, and fulvestrant combined with trastuzumab and neratinib.³⁵

There are other approaches to target ERBB2-mutant cancers that have shown promising clinical activity. A phase II basket trial of ado-trastuzumab emtansine (T-DM1), an antibody-drug conjugate linking trastuzumab with the antimicrotubule agent emtansine, reported an ORR of 44% in ERBB2-mutant NSCLC.³⁷ More recently, a first-in-human phase I trial of trastuzumab deruxtecan, an antibody-drug conjugate linking trastuzumab to a topoisomerase I inhibitor payload, demonstrated an ORR of 72% in ERBB2-mutant NSCLC.³⁸ The antitumor activity of trastuzumab deruxtecan was confirmed by the DESTINY-01 Lung trial that reported an ORR of 62% with a median PFS of 14 months.³⁹ The proposed mechanism for this observed antitumor activity of HER2-targeted antibody drug conjugates is related to enhanced ubiquination internalization of HER2 homodimers or heterodimers related to activating ERBB2 mutations that can be enhanced with cotreatment with irreversible HER2 tyrosine kinase inhibitors.⁴⁰

There are several limitations of our study. Only selected ERBB2 SNVs and indels were eligible (Appendix Table A1) on the basis of available levels of evidence for clinical actionability when the protocol was developed in 2015. More recent high-throughput preclinical studies found differences in transforming activities and sensitivities to HER2-targeted inhibitors for different ERBB2 variants.⁴¹ For example, ERBB2 exon 20 insertions were more sensitive to afatinib and neratinib, and L755 variants were more resistant to afatinib and neratinib. In our study, none of the six patients with L755S mutations showed evidence of antitumor activity. With limited numbers of patients enrolled across diverse tumor histologies, we cannot draw any definitive conclusions about the differential activity of afatinib in ERBB2 cancers according to tumor type and/or ERBB2 variants. We did not include prophylactic antidiarrheal therapy with the initiation of afatinib therapy. Although the safety profile and rate of treatment discontinuation because of AEs (11%) were similar to that seen in other trials with afatinib, discontinuation in the SUMMIT basket trial with neratinib was only 2.8%. Finally, because of the minimal antitumor activity observed, our analysis of comutation associated with sensitivity or resistance to afatinib was limited.

To conclude, afatinib did not meet the prespecified threshold for antitumor activity in ERBB2-mutated advanced solid tumors. The response observed in EMPD, a rare tumor type with no standard therapy, is notable and warrants further investigation. Future studies will evaluate the antitumor activity of irreversible HER2 kinase inhibitors for ERBB2-mutant solid tumors in combination with other therapeutic approaches, such as endocrine therapy and HER2 monoclonal antibodies in ER+ breast cancers, and HER2-antibody drug conjugates in NSCLC and other solid tumors.

APPENDIX

TABLE A1.

ERBB2 Variants Eligible for Study Inclusion⁴²

AUTHOR CONTRIBUTIONS

Administrative support: Jeffrey A. Moscow, David R. Patton, Lyndsay N. Harris, Keith T. Flaherty

Provision of study materials or patients: Kari B. Wisinski, Eddy S. Yang, David R. Patton, Stanley R. Hamilton

Collection and assembly of data: Edith P. Mitchell

Data analysis and interpretation: Philippe L. Bedard, Eddy S. Yang, Edith P. Mitchell, Jeffrey A. Moscow, Robert J. Gray, Victoria Wang, Lyndsay N. Harris, Alice P. Chen, Keith T. Flaherty

Manuscript writing: All authors

Final approval of manuscript: All authors

Accountable for all aspects of the work: All authors

AUTHORS' DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST

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