Abstract
Background
Amplification/overexpression of the human epidermal growth factor receptor 2 (HER2) gene drives cell proliferation, differentiation, and migration of breast cancer. However, HER2-targeted therapies are not standard treatment for HER2-positive non-breast solid tumors currently. This phase II open-label basket trial evaluated pyrotinib’s efficacy and safety in patients with non-breast solid tumors.
Methods
Patients with previously treated HER2-positive advanced non-breast solid tumors were enrolled at Zhongshan Hospital, Fudan University. All participants received pyrotinib in 21-day cycles. Primary endpoint was objective response rate (ORR) at 6 weeks, assessed per RECIST version 1.1. Circulating tumor DNA (ctDNA) analysis was conducted to identify biomarkers of efficacy.
Results
Fifty-three patients were enrolled and 51 evaluable for efficacy analysis. The median follow-up was 32.2 months. ORR was 18.9% (95% CI: 10.2%-31.7%) and disease control rate was 73.6% (95% CI: 60.1%-84.2%). Median progression-free survival (mPFS) was 5.1 (95% CI: 4.2-8.1) months and median overall survival (mOS) was 17.2 (95% CI: 16.2-33.2) months. Patients with colorectal cancer had the highest ORR and the longest mOS (33.2 months, 95% CI: 14.9-51.5). Among patients with HER2 overexpression, those with immunohistochemistry 3+ had longer mPFS and mOS. Sixteen patients required dose reductions due to grade 3 adverse events (AEs); no ≥grade 4 AEs occurred. Analysis of ctDNA revealed that patients with progression disease had higher mutation frequency, more diverse mutational profiles, and higher copy number burden.
Conclusion
Pyrotinib demonstrated a favorable safety profile and modest efficacy in patients with previously treated HER2-positive advanced non-breast solid tumors.
Keywords: pyrotinib, HER2-directed agents, basket trial, circulating tumor DNA
Implications for Practice.
Amplification/overexpression of the human epidermal growth factor receptor 2 (HER2) gene drives cell proliferation, differentiation, and migration of breast cancer. However, HER2-targeted therapies are not standard treatment for HER2-positive non-breast solid tumors currently. This phase 2, open-label basket trial demonstrated favorable clinical efficacy and a comparable safety profile of pyrotinib in previously treated HER2-positive non-breast solid tumors. Our study results provided a potential treatment option for later-line therapy of HER2-positive solid tumors, especially colorectal cancer, offering a valuable alternative for patients with limited treatment options.
Introduction
Human epidermal growth factor receptor 2 (HER2) overexpression or amplification is commonly observed in several cancers, including breast, gastric cancer (GC), and colorectal cancer (CRC), driving uncontrolled cell division, invasion, and metastasis.1 Despite progress in breast cancer, HER2-targeted therapies for non-breast solid tumors with HER2-altered remain underexplored.2,3
HER2-targeted therapies, including trastuzumab, lapatinib, have significantly improved outcomes in HER2-positive cancers by blocking HER2 signaling, reducing tumor cell growth, enhancing immune surveillance, and increasing sensitivity to chemotherapy.3,4 Recently, novel HER2-targeted ADCs (ARX788, T-DXd, T-DM1) and bispecific antibodies (zanidatamab) show efficacy in refractory HER2-positive malignancies, particularly gastric and breast cancers.3–9 Pyrotinib, an irreversible pan-HER tyrosine kinase inhibitor (TKI), offers broad downstream blockade and sustained inhibition of HER2 signaling by targeting multiple HER family receptors through covalent binding.10 PHOEBE and PHILA have demonstrated its efficacy in metastatic HER2-positive breast cancer, both as monotherapy and in combination with other agents, even in patients previously treated with trastuzumab.11,12
This open-label, phase II basket trial was conducted to evaluate the efficacy and safety of pyrotinib in patients with previously treated HER2-positive advanced non-breast solid tumors.
Study design
This phase II, open-label basket trial involved patients with HER2-positive unresectable or advanced non-breast solid tumors who had experienced progression following prior therapy at Zhongshan Hospital, Fudan University, between April 2, 2021 and August 3, 2023. The study was reviewed and approved by the Ethics Committee of Zhongshan Hospital, Fudan University (Approval Number: B2021-168) and conducted in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines. Written informed consent was obtained from all patients before enrollment. The trial was registered with chictr.org.cn (ID: ChiCTR2100046381).
Study population
Patients with histologically or cytologically confirmed HER2-positive solid tumors were enrolled in the study, stratified into 5 cohorts based on the underlying diagnosis: advanced GC or gastroesophageal junction adenocarcinoma, metastatic CRC, advanced esophageal squamous cell carcinoma or adenocarcinoma, advanced lung cancer (LC), and other non-breast solid malignancies. HER2 positivity was defined as HER2 overexpression/amplification and HER2 mutation. For GC and other tumor types, HER2 overexpression or amplification was determined according to the ToGA trial criteria, while for CRC, diagnostic criteria were in accordance with HERACLES trial. HER2 mutations were detected by next-generation sequencing (NGS), polymerase chain reaction, Sanger sequencing, mass spectrometry, or other validated methods. The inclusion criteria were as follows: (1) patients aged 18-75 years; (2) an Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0-1; (3) a pathologically confirmed diagnosis of gastric or gastroesophageal junction adenocarcinoma, RAS wild-type and BRAF wild-type colorectal adenocarcinoma, esophageal squamous cell carcinoma or adenocarcinoma, advanced LC, or other non-breast solid tumors; (4) for cohort of gastric or gastroesophageal junction adenocarcinoma, patients should failed to prior trastuzumab-based treatment; (5) at least one prior standard palliative chemotherapy regimen for patients with metastastic or advanced disease; (6) at least one measurable lesion according to RECIST 1.1; and (7) adequate bone marrow, liver, and renal function. For patients with LC, HER2 mutation status was essential to be tested before enrollment, while the detection of HER2 expression was not required according to clinical routine practice. Exclusion criteria included active or untreated brain metastases, spinal cord compression, carcinomatous meningitis, or other CNS disorders identified by CT or MRI during screening. Patients with other primary malignant tumors were also excluded, except those with cutaneous squamous carcinoma in situ diagnosed within the past 5 years. Prior treatment with HER2-TKIs was not permitted. Additionally, for the CRC cohort, patients harboring RAS mutations were excluded.
Procedure
All participants received pyrotinib orally at a dose of 400 mg/day within 30 minutes after breakfast in a continuous 21-day treatment cycle. Pyrotinib dose adjustments were permitted in decrements of 400 mg, 320 mg, 240 mg, and 160 mg. Permanent discontinuation of pyrotinib was required for Grade 4 diarrhea. For Grade 3 diarrhea, or Grade 1-2 diarrhea with complications (such as severe abdominal cramping, ≥Grade 2 nausea or vomiting, dehydration, or neutropenia), administration was suspended. Treatment resumed at the next lower-dose level only after symptoms recovered to Grade 0-1 and all complications had fully resolved. Investigators could initiate a further dose reduction by one decrement (to a minimum of 160 mg) if a participant subsequently experienced either clinically uncontrollable Grade 3 or higher diarrhea (ie, persistent after ≤14 days of treatment or observation, or recurring ≥2 times), Grade 1-2 diarrhea with complications, or other adverse events (AEs) of ≥Grade 2. Loperamide (4 mg 3 times daily for weeks 1-2, then 4 mg twice daily in week 3, and subsequently as needed up to 16 mg/day) was allowed for prophylactic use.
Biomarker analysis
Peripheral blood samples from the enrolled patients were subjected to NGS targeting 769 cancer-related genes at Genecast Biotechnology Co., Ltd, a CAP-certified laboratory. Genomic DNA from tumor tissues was extracted using TIANamp Genomic DNA Kit (TIANGEN), while germline DNA from peripheral blood cells was isolated using TGuide S32 Magnetic Blood Genomic DNA Kit (TIANGEN). DNA concentration was measured with Qubit dsDNA HS (High Sensitivity) Assay Kit (Themo Fisher), and DNA quality was evaluated using Agilent 2100 BioAnalyzer (Agilent).
Targeted region enrichment was performed using HyperCap Target Enrichment Kit (Roche), with hybridization and washing carried out according to the manufacturer’s protocol. The captured libraries were sequenced on the Illumina Novaseq 6000 platform, generation 150 bp paired-end reads. Raw sequencing data underwent quality control using Trimmomatic (v0.36),13 followed by alignment to the human reference genome (hg19) using the BWA aligner (v0.7.17).14 Duplicate reads were marked using Picard (v2.23.0), and the resulting BAM files were used for downstream analyses. Somatic and germline variants, including single-nucleotide variants, insertions and deletions (INDELs), and complex mutations, were identified using VarDict (v1.5.1)15 and FreeBayes (v1.2.0).16
Outcomes
The primary endpoint was the 6-week overall response rate (ORR), defined as the proportion of patients achieving a confirmed complete response (CR) or partial response (PR) per RECIST 1.1. Tumor imaging assessments were performed every 6 ± 1 weeks. All patients achieving CR/PR at the first assessment (Week 6) underwent confirmatory imaging ≥4 weeks later (typically at the next scheduled evaluation), in accordance with RECIST 1.1 criteria. Secondary endpoints included progression-free survival (PFS), defined as the time from the first dose to objective disease progression or death from any cause, regardless of treatment discontinuation or subsequent therapy; overall survival (OS), defined as the time from the first dose to death from any cause; disease control rate (DCR), defined as the proportion of patients achieving a best overall response of CR, PR, or stable disease (SD); and safety, assessed by the incidence and severity of AEs. according to CTCAE version 5.0.
Statistics analysis
This study utilized a Minimax Simon’s 2-stage design with a null hypothesis (H0) response rate of 10%, an alternative hypothesis (H1) response rate of 30%, a 1-sided α of 0.10, and 80% power. In the first stage, 7 patients were enrolled per cohort. If ≤1 patient achieved a CR or PR, the cohort was terminated. If more than 1 patient achieved a response, the cohort progressed to the second stage, enrolling an additional 10 patients for a total of 17 patients per cohort. If ≤4 of the 17 patients achieved CR or PR, the treatment was deemed ineffective. Each cohort advancing to the second stage continued enrollment until at least 17 patients per cohort were reached.
Efficacy was assessed in all patients who received at least one dose of pyrotinib and underwent disease re-evaluation according to protocol. Safety was evaluated in all patients who received at least one dose of pyrotinib. The median progression-free survival (mPFS) and median overall survival (mOS) were estimated using the Kaplan–Meier method, with 95% CIs calculated using the Brookmeyer–Crowley method. The Clopper–Pearson method was employed to determine 95% CIs for the ORR and DCR. Subgroup analysis was conducted for different tumor disease populations. Spearman’s correlation analysis examined the relationship between copy number (CN) and efficacy. All statistical analyses were conducted using SAS version 9.4, with statistical significance set at P < .05.
Results
Study population
Between April 2, 2021 and August 3, 2023, a total of 58 patients were screened, of which 53 were enrolled in the study. The reasons for exclusion included an ECOG Performance Status score >1 (n = 3) and HER2-negative status confirmed by re-biopsy (n = 2). Although a repeat biopsy was not required as part of the eligibility criteria, 2 patients underwent re-biopsy at the discretion of the treating physician to confirm HER2 status due to clinical uncertainty. Given the central role of HER2 positivity in defining eligibility for anti-HER2 therapy in this study, and to ensure both scientific validity and patient safety, these patients were ultimately excluded. The cohort consisted of patients with various types of cancer: 18 with CRC, 17 with GC, 7 with LC, 2 with gallbladder cancer, 2 with bladder cancer, and 1 each with bile duct, cervical, ovarian, pancreatic, esophageal, and endometrial cancer, as well as 1 with mediastinal neuroendocrine carcinoma. Among the 53 enrolled patients, HER2 IHC 3+ expression was in 32 patients, HER2 IHC 2+ expression was in 14 patients, and 7 patients with HER2 exon 20 mutations (Table 1). The median age of the cohort was 64 years (range: 30-73), with 30 patients (56.5%) being male. Eighteen patients (35.0%) had received more than 2 prior lines of therapy, with a median of 2 lines (Table 1). Six patients (11.3%) received pyrotinib as second-line therapy, while 47 patients (88.7%) received it as third-line or later treatment. Additionally, 28 patients (52.8%) had previously received HER2-targeted therapy: trastuzumab (3 with CRC, 17 with GC, 1 with esophageal cancer), trastuzumab plus pertuzumab (1 with CRC, 1 with cholangiocarcinoma), and disitamab vedotin (2 with LC).
Table 1.
Demographics and baseline clinical characteristics.
| All (n = 53) | CRC (n = 18) | GC (n = 17) | LC (n = 7) | Others (n = 11) | |
|---|---|---|---|---|---|
| Age, years, median (range, 30–73) | 63.5 | 57.0 | 61.0 | 64.0 | 68.0 |
| Gender | |||||
| Male, N (%) | 30 (56.6) | 10 (55.6) | 10 (58.8) | 2 (28.6) | 8 (72.7) |
| Female, N (%) | 23 (43.4) | 8 (44.4) | 7 (41.2) | 5 (71.4) | 3 (27.3) |
| ECOG Performance Status score, N (%) | |||||
| 0 | 18 (34.0) | 8 (44.4) | 6 (35.3) | 2 (28.6) | 2 (18.2) |
| 1 | 35 (66.0) | 10 (55.6) | 11 (64.7) | 5 (71.4) | 9 (81.8) |
| HER2 IHC status, N (%) | |||||
| IHC 3+ | 32 (60.4) | 14 (26.4) | 12 (70.6) | 0 (0.0) | 6 (54.5) |
| IHC 2+ | 14 (26.4) | 4 (7.6) | 5 (29.4) | 0 (0.0) | 5 (45.5) |
| HER2 20 exon mutate | 7 (13.2) | 0 (0.0) | 0 (0.0) | 7 (100.0) | 0(0.0) |
| Prior therapy lines, N (%) | |||||
| 1, N (%) | 6 (11.3) | 0 (0.0) | 2 (11.8) | 0 (0.0) | 4 (36.3) |
| 2, N (%) | 29 (54.7) | 11 (61.1) | 7 (41.2) | 6 (85.7) | 5 (45.5) |
| 3, N (%) | 13 (24.5) | 6 (33.3) | 5 (29.4) | 0 (0.0) | 2 (18.2) |
| 4, N (%) | 3 (5.7) | 0 (0.0) | 2 (11.8) | 1 (14.3) | 0 (0.0) |
| 5, N (%) | 2 (3.8) | 1 (5.6) | 1 (5.8) | 0 (0.0) | 0 (0.0) |
| Prior HER2 therapy, n (%) | |||||
| No | 28 (52.8) | 14 (77.8) | 0 (0) | 5 (71.4) | 9 (81.8) |
| Yes | 25 (47.2) | 4 (22.2) | 17 (100) | 2 (28.6) | 2 (18.2) |
| Trastuzumab | 21 (39.6) | 3 (16.7) | 17 (100) | 0 (0) | 1 (9.1) |
| Trastuzumab+Pertuzumab | 2 (3.8) | 1 (5.6) | 0 (0) | 0 (0) | 1 (9.1) |
| ADC | 2 (3.8) | 0 (0) | 0 (0) | 2 (28.6) | 0 (0) |
Other malignancies included 2 cases of gallbladder cancer, 2 cases of bladder cancer, 1 case of bile duct cancer, 1 case of cervical cancer, 1 case of ovarian cancer, 1 case of pancreatic cancer, 1 case of esophageal cancer, 1 case of endometrial cancer, and 1 case of mediastinal neuroendocrine carcinoma. Additionally, there were cases of colorectal cancer (CRC), gastric cancer (GC), and lung cancer (LC).
Abbreviations: ECOG, Eastern Cooperative Oncology Group; IHC, immunohistochemistry; HER2, Human Epidermal Growth Factor Receptor 2.
Outcomes
The median follow-up was 32.2 months (range, 10.5-40.2 months). Among the 53 patients treated, 51 were evaluable for response, while 2 withdrew prematurely due to AEs. Until October 14, 2024, 3 patients remained on treatment, and 48 had progression disease (PD) (18 patients were alive, and 30 had died due to PD) (Figure 1). A total of 10 patients (19.6%) had PR as the best response, while no patients had CR.
Figure 1.
Patient flowchart. Flow chart illustrating the enrolment of HER2-positive patients.
The ORR was 18.9% (95% CI: 10.2%, 31.7%) in the evaluable population. The DCR was 73.6% (95% CI: 60.1%, 84.2%). The mPFS and mOS were 5.1 (95% CI: 4.2%, 8.1%) months and 17.2 (95% CI: 16.2%, 33.2%) months, respectively (Table 2). Among the 7 patients with primary LC, only one achieved PR, leading to the termination of the cohort. Due to slow enrollment, the esophageal cancer cohort was merged with the cohort for other malignancies before study completion. Subgroup analysis revealed that the CRC cohort had the highest ORR (22.2%, 95% CI: 6.4%, 47.6%) and the longest mOS (33.2, 95% CI: 14.9, 51.5 months). Median PFS and mOS in all patients with measurable lesions and in subgroups were shown in Figure 2. Maximum changes from baseline in measurable target lesions among patients with efficacy evaluation were shown in Figure 3.
Table 2.
Clinical response to pyrotinib in patients with HER2-positive solid tumors.
| Best response | All (n = 51) | CRC (n = 18) | GC (n = 16) | LC (n = 7) | Others (n = 10) |
|---|---|---|---|---|---|
| CR, n | 0 | 0 | 0 | 0 | 0 |
| PR n | 10 | 4 | 3 | 1 | 2 |
| SD n | 29 | 10 | 10 | 4 | 5 |
| PD, n | 12 | 4 | 3 | 2 | 3 |
| ORR, n (95% CI) | 18.9 (10.2-31.7) | 22.2 (6.4-47.6) | 17.7 (6.3-35.8) | 14.3 (2.6-51.3) | 18.2 (3.2-43.8) |
| DCR, n (95% CI) | 73.6 (60.1-84.2) | 77.8 (52.4-93.6) | 76.5 (52.7-91.5) | 71.4 (35.9-91.8) | 63.6 (36.4-84.8) |
| mPFS, months (95% CI) | 5.1 (4.2-8.1) | 5.6 (3.6-7.3) | 7.0 (4.5-9.4) | 4.1 (3.5-4.7) | 3.8 (1.7-NA) |
| mOS, months (95% CI) | 17.2 (16.2-33.2) | 33.2 (14.9-51.5) | 16.4 (8.8-34.4) | 22.3 (5.1-49.5) | 16.5 (7.4-NA) |
Others included 2 with gallbladder cancer, 2 with bladder cancer, 1 with bile duct cancer, 1 with cervix uteri cancer, 1 with ovarian cancer, 1 with pancreatic cancer, 1 with esophageal cancer, 1 with endometrial cancer, and 1 with mediastinum neuroendocrine carcinoma (Colorectal cancer, CRC; gastric cancer, GC; lung cancer, LC).
Abbreviations: CI, confidence interval; CR: complete response; DCR, disease control rate; mPFS, median progression free survival; mOS, median overall survival; ORR, objective response rate; PD, progressive disease; PR, partial response; SD, stable disease.
Figure 2.
The Kaplan–Meier estimates analysis of PFS and OS. (A) KM analysis of PFS and OS in all patients with measurable lesions. (B) Subgroup KM analysis of PFS and OS.
Figure 3.
Maximum changes from baseline in measurable target lesions among patients with CRC, GC, LC, and other malignancies during the treatment.
Safety
Overall, 18 patients (34.0%) experienced Grade 3 AEs. Diarrhea was the most common AE, reported in 51 patients (96.2%), and was the leading cause of dose reductions. Other frequent AEs included nausea (27 patients, 50.9%) and leukopenia (12 patients, 22.6%). Sixteen patients (30.2%) required dose reductions due to Grade 3 AEs, most commonly diarrhea (14 patients, 26.4%), with one case each of Grade 3 vomiting, fatigue, and oral ulcer. Management of diarrhea followed a predefined protocol: patients experiencing Grade 3 diarrhea or Grade 1-2 diarrhea with complications (eg, abdominal cramping, ≥Grade 2 nausea or vomiting, ECOG Performance Status score decline, fever, neutropenia, or dehydration) underwent temporary interruption, followed by resumption at a reduced dose (400 mg, 320 mg, 240 mg, 160 mg) once symptoms resolved to Grade 0-1. Loperamide (began with 4 mg 3 times a day and up to 16 mg/day) was permitted for prophylactic or therapeutic use. Despite these measures, Grade 3 AEs recurred in 2 patients, resulting in treatment discontinuation. No treatment-related mortality occurred (Table 3).
Table 3.
Incidence of drug-related adverse events.
| Adverse event, n (%) | All | Grade 1-2 | Grade 3 |
|---|---|---|---|
| Leading to discontinuation | 2 (3.8) | 0 (0) | 2 (3.8) |
| Leading to dose modification | 16 (30.2) | 0 (0) | 16 (30.2) |
| Diarrhea | 51 (96.2) | 37 (69.8) | 14 (26.4) |
| Vomiting | 27 (50.9) | 25 (47.2) | 2 (3.8) |
| Leukopenia | 12 (22.6) | 12 (22.6) | 0 (0) |
| Neutropenia | 10 (18.9) | 10 (18.9) | 0 (0) |
| Nausea | 8 (15.1) | 7 (13.2) | 1 (1.9) |
| Fatigue | 8 (15.1) | 7 (13.2) | 1 (1.9) |
| Elevated alanine aminotransferase | 6 (11.3) | 6 (11.3) | 0 (0) |
| Elevated aspartate aminotransferase | 6 (11.3) | 6 (11.3) | 0 (0) |
| Anemia | 4 (7.5) | 4 (7.5) | 0 (0) |
| Rash | 3 (5.7) | 3 (5.7) | 0 (0) |
| Oral ulcer | 2 (3.8) | 1 (1.9) | 1 (1.9) |
Genomic profiles
Biomarker analysis was conducted on the ctDNA of 35 patients using NGS. After excluding samples from 4 patients with failed sequencing, samples from 31 patients remained for analysis (8 PR, 16 SD, 7 PD). The most frequently altered genes in ctDNA were P53 (50%), APC (35%), MLH1 (15%), EGFR (15%), ERBB2 (15%), PIK3CA (15%), and CARD11 (10%), primarily affecting the RTK-RAS, Notch, and WNT signaling pathways (Supplementary Figure S1). Mutation profile analysis revealed that patients in the PD group had a higher number and diversity of gene mutations, including somatic nonsynonymous mutations, frameshift insertions, and frameshift deletions, compared to the patients in PR group (Supplementary Figure S1). Additionally, patients in the PD group had a significantly higher frequency of somatic mutations and frameshift alterations. Copy number variants (CNV) analysis indicated that ERBB2 (45%) had the highest frequency of CNVs, followed by GNAS (25%), AURKA (25%), TOP1 (25%), RARA (25%), and RAC1 (20%). The CNV burden was significantly higher in patients in the PD group compared to the PR group (P < .05), though no significant difference was observed in the CN increase burden between groups (Supplementary Figure S1).
Genomic alteration profiles and clinical outcomes
Log-rank test results showed no significant differences in mPFS (P = .22) or mOS (P = .27) between patients with HER2 CN <10 and those with CN ≥10. Patients with CN <10 had an ORR of 37.5%, and patients with CN ≥10 had an ORR of 14.3%. However, this difference was not statistically significant (P = .45) (Supplementary Figure S2). Among the 31 patients, 10 patients had known genetic alterations potentially associated with resistance to anti-HER2 therapy, including PIK3CA mutations, KRAS mutations, NRAS mutations, BRAF mutations, SRC mutations, and PTEN loss. No significant differences were observed between these groups in ORR (20.0% vs 28.6%, P = 1.00), DCR (60.0% vs 85.7%, P = .22), mPFS (5.0 vs 5.1 months, P = .39), or mOS (15.1 vs 22.5 months, P = .65).
Discussion
Although the primary endpoint was not met, pyrotinib achieved meaningful disease control in heavily pretreated HER2-positive tumor, especially in CRC subgroup. Statistically, we found that the 95% CI for the overall ORR is 10.2% to 31.7%, with the lower bound being higher than the historical control of 10%. Pyrotinib showed superiority to those reported in later-line standards of care such as TAS-102 in CRC (median PFS: 2.0 months),17 docetaxel in NSCLC (median PFS: 2.1 months),18 irinotecan in GC (median PFS: 2.5 months).19
Our study adopted the same HER2-positive definition as MyPathway and SUMMIT trials, including patients with either HER2 mutations or amplifications. Preclinical and clinical evidence suggests that HER2 amplification may preferentially occur on pre-existing HER2-mutated alleles, which may indicate a potential synergy between mutations and CN gains.20 The inclusion of diverse tumor types in this basket trial inevitably introduces biological heterogeneity. HER2 aberrations vary substantially across malignancies. In CRC, HER2 positivity mainly arises from high protein expression or gene amplification, and responses to the anti-HER2 therapy efficacy are strongly correlated with expression levels.21 In contrast, HER2-positive NSCLC is often driven by activating mutations, especially exon 20 insertions, which respond poorly to antibody-based therapies and generally require specific TKI or ADC. GC exhibits pronounced intratumoral HER2 heterogeneity as well as the inconsistency of expression between primary and metastatic lesions. These biological distinctions likely underlie the variable efficacy observed across tumor types in this study and in other basket trials.2,22–24 Although basket trials have the inherent limitation of overlooking heterogeneity among tumor types and genomic contexts, they still allow the efficient identification of patient subgroups with meaningful responses, particularly in rare HER2-driven cancers.
Studies reveal variable efficacy of HER2-targeted therapies across solid tumor types.22,25 In this study, the most favorable efficacy was observed in CRC subgroup, with an ORR of 22.2% and mOS of 33.2 months, which was consistent with our observational study.26 It might be attributed to higher HER2 amplification rates and a more permissive tumor microenvironment, which supports drug penetration and receptor inhibition. This less hostile tumor microenvironment could facilitate a more effective response to pyrotinib by allowing better drug penetration and sustained receptor inhibition.27
Limited efficacy in LC cohort (1 PR), likely due to lung cancer’s complex genomic landscape (eg, EGFR/KRAS mutations) conferring HER2 therapy resistance. All enrolled patients with LC harbored HER2 mutations rather than amplifications, suggesting that pyrotinib may have limited efficacy against exon 20 insertion mutations, and more selective HER2 inhibitors effective in this context. Zongertinib (BI 1810631), a selective covalent inhibitor targeting the HER2 tyrosine kinase domain (including exon 20 insertions) while sparing wild-type EGFR, has demonstrated promising early-phase efficacy in HER2-mutant NSCLC.28 Mechanistic differences exist among HER2-targeting TKIs (eg, zongertinib vs pyrotinib), potentially conferring distinct efficacy advantages across tumor types. In GC, the efficacy of pyrotinib exceeded that of conventional chemotherapy but remained inferior to T-DXd.29 These findings are consistent with the limited efficacy of other HER2-targeted agents, such as lapatinib and T-DM1, in trastuzumab-resistant GC, highlighting the challenges posed by intratumoral HER2 heterogeneity and multifactorial resistance mechanisms. PR was also observed in individual cases of bladder and gallbladder cancers, supporting current guidelines that recommend anti-HER2 therapies as later-line options for these tumor types.
No specific biomarkers correlated with pyrotinib efficacy in HER2-positive solid tumors were identified in the current study, including HER2 CNV. This observation contrasts with several previous reports but may be attributable to multiple factors. First, HER2 CNV was assessed using ctDNA instead of contemporaneous tumor tissue. For the enrolled patients who had received multiple prior lines of therapy, which may have introduced false negatives. Second, biological variation in ctDNA shedding between tumor types may affect detectability, as different malignancies release tumor DNA into circulation at variable rates.30 Finally, the sample size of our ctDNA subgroup analysis was limited, which may result in limited statistical power.
However, the PD group exhibited a higher CNV burden and greater diversity in somatic mutations compared to PR. Higher frequencies of mutated genes are linked to tumor resistance to pyrotinib. Elevated genomic instability, including CNV burdens, is a key feature of therapeutic resistance in various cancers.22 Circulating tumor DNA analysis revealed frequent mutations in P53, APC, MLH1, EGFR, ERBB2, PIK3CA, and CARD11, which were involved in critical cellular signaling pathways regulating tumorigenesis and therapeutic resistance.31–33 Exploratory analysis compared efficacy between patients harboring key HER2 resistance mutations versus others. However, only 10 patients in the ctDNA cohort harbored such mutations, and therefore these negative results should be interpreted with caution. These preliminary findings require validation in larger, prospective datasets.
This study has several limitations, including its small sample size, heterogeneity of enrolled patients, single center and non-control study, which may have influenced the efficacy analysis to some extent. Larger multicenter validation studies are needed.
In conclusion, this phase 2, open-label basket trial demonstrated favorable clinical efficacy and a comparable safety profile of pyrotinib in HER2-positive non-breast solid tumors. These results suggest that pyrotinib could serve as a valuable treatment option for later-line therapy in HER2-positive solid tumors especially in CRC. Pyrotinib’s oral administration and favorable toxicity profile make it a promising backbone for combination anti-HER2 therapy. Future studies could explore synergistic combinations to enhance efficacy.
Supplementary Material
Acknowledgments
The authors are grateful to the patients, families, and study teams who participated in the cohort study.
Contributor Information
Haojie Zhou, Department of Oncology, Zhongshan Hospital, Fudan University, Shanghai 200030, China; Department of Oncology, Central Hospital of Xuhui District, Shanghai 200030, China.
Minzhi Lv, Department of Cancer Prevention and Sreening, Zhongshan Hospital, Fudan University, Shanghai 200030, China; Department of Biostatistics, Zhongshan Hospital, Fudan University, Shanghai 200030, China; Department of Evidence-Based Medicine, Fudan University, Shanghai 200030, China.
Wei Li, Department of Oncology, Zhongshan Hospital, Fudan University, Shanghai 200030, China.
Yan Wang, Department of Oncology, Zhongshan Hospital, Fudan University, Shanghai 200030, China.
Jing Wu, Department of Oncology, Zhongshan Hospital, Fudan University, Shanghai 200030, China.
Qing Liu, Department of Oncology, Zhongshan Hospital, Fudan University, Shanghai 200030, China.
Tianshu Liu, Department of Oncology, Zhongshan Hospital, Fudan University, Shanghai 200030, China; Department of Cancer Prevention and Sreening, Zhongshan Hospital, Fudan University, Shanghai 200030, China; Department of Evidence-Based Medicine, Fudan University, Shanghai 200030, China.
Qian Li, Department of Medical Oncology, Shanghai Geriatric Medical Center, Shanghai 201100, China.
Author contributions
Haojie Zhou (Conceptualization, Formal analysis, Investigation, Writing—original draft), Minzhi Lv (Data curation, Methodology, Visualization, Writing—original draft), Wei Li (Investigation, Resources), Yan Wang (Software, Validation), Jing Wu (Project administration, Writing—review & editing), Qing Liu (Formal analysis, Resources), Tianshu Liu (Conceptualization, Supervision, Writing—review & editing), and Qian Li (Funding acquisition, Supervision, Writing—review & editing)
Supplementary material
Supplementary material is available at The Oncologist online.
Funding
This study was funded by the Special Clinical Research Program of Shanghai Municipal Health Commission Health Industry (No. 202040222).
Conflicts of interest
None declared.
Data availability
All data generated or analyzed during this study are included in this published article.
References
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Data Availability Statement
All data generated or analyzed during this study are included in this published article.