A New Hope: Dual Human Epidermal Growth Factor Receptor 2 Blockade and Chemotherapy in Human Epidermal Growth Factor Receptor 2-Amplified Colorectal Cancer – A Case Report and Literature Review

Abstract

Introduction

Monoclonal antibodies targeting epidermal growth factor receptors (EGFRs) are currently the preferred targeted therapeutic agents for RAS wild-type, left-sided metastatic colorectal cancer (mCRC). Nonetheless, certain molecular alterations within mCRC confer resistance to anti-EGFR monoclonal antibody therapy, notably alterations involving human epidermal growth factor receptor 2 (HER2). Colorectal cancer (CRC) characterized by HER2 amplification or overexpression may have markedly different prognoses than HER2-negative CRC does. Recent clinical trials have demonstrated that dual HER2 blockade leads to significant improvements in clinical outcomes for these patients.

Case Presentation

In this study, we present a case in which HER2-positive mCRC was successfully treated with HER2-targeted agents combined with chemotherapy, resulting in favorable clinical outcomes.

Conclusion

Dual HER2-targeted therapy combined with chemotherapy is a promising strategy for HER2-positive mCRC patients with good performance status. This approach warrants validation in large-scale clinical trials to confirm its efficacy.

Introduction

Colorectal cancer (CRC) is among the most prevalent gastrointestinal malignancies worldwide. For patients with advanced disease, treatment strategies are increasingly reliant on molecular subtyping to guide precision therapy. Anti-epidermal growth factor receptor (EGFR) monoclonal antibodies, such as cetuximab, represent a standard therapeutic option for patients with metastatic CRC (mCRC) harboring wild-type RAS genes (including KRAS and NRAS), significantly improving survival outcomes in this subset [1–3]. However, clinical evidence has revealed that not all patients with RAS wild-type tumors benefit from treatment with cetuximab, suggesting the involvement of other critical resistance mechanisms or predictive biomarkers that remain incompletely characterized. While established resistance factors include mutations such as BRAF V600E, these mutations fail to account for all instances of treatment failure [4].

Emerging evidence from both preclinical investigations and preliminary clinical studies in recent years highlights the significant role of human epidermal growth factor receptor 2 (HER2, also known as ERBB2) mutation in CRC. Research has consistently demonstrated that HER2-positive status is strongly associated with primary resistance to the anti-EGFR monoclonal antibody cetuximab [5–7]. HER2 positivity itself may serve as an independent predictor of poor prognosis in advanced CRC patients. Based on these findings, it is hypothesized that HER2-positive CRC constitutes a distinct molecular and biological subtype. Consequently, gaining deeper mechanistic insights into the specific contributions of HER2 signaling to CRC pathogenesis, metastasis, and therapeutic resistance is crucial. Developing and refining effective treatment strategies specifically for patients with HER2-positive mCRC represent a high-priority research avenue that urgently warrants further exploration within the field.

In this study, we report a case of HER2-positive mCRC that was effectively managed using a combination of HER2-targeted therapies and chemotherapy, resulting in favorable clinical outcomes. The findings of this study may provide valuable insights for the treatment of HER2-positive advanced CRC.

Case Presentation

A 65-year-old male patient presented with a 1-week history of paroxysmal abdominal pain associated with defecation difficulty in November 2014. Colonoscopy revealed a sigmoid colon mass, and subsequent biopsy demonstrated adenocarcinoma. Subsequent abdominal CT and PET-CT revealed malignant tumor lesions at the descending colon junction with proximal intestinal obstruction and liver metastasis. Stent placement was successfully performed at the colon stricture before antitumor treatment. Molecular profiling revealed a wild-type status for KRAS, NRAS, and BRAF and microsatellite stability. The patient received a modified FOLFOX regimen plus cetuximab every 2 weeks. Each treatment cycle included intravenous cetuximab (900 mg), oxaliplatin (150 mg), and leucovorin (720 mg), followed by fluorouracil with a bolus of 720 mg and a subsequent 46-h continuous infusion of 4,320 mg via pump. Following 4 cycles of neoadjuvant therapy, the patient underwent surgical resection of the primary colon tumor and hepatic metastases on February 4, 2015. The surgery achieved R0 resection, with the final postoperative pathology confirming the diagnosis of colorectal adenocarcinoma with synchronous liver metastases. As adjuvant therapy, the patient completed six cycles of the modified FOLFOX regimen plus cetuximab from the postoperative period until June 2015. Recurrent disease was first identified in December 2016 by an abdominal CT scan, which revealed multiple metastases, including local recurrence in the liver, peritoneal carcinomatosis, and omental deposits. The patient underwent six cycles of a biweekly (q2w) regimen combining FOLFIRI (irinotecan 320 mg, leucovorin 720 mg, fluorouracil 720 mg IV bolus plus 4,320 mg over 46 h via pump) and bevacizumab (350 mg) with a best radiographic response of partial response. Following tumor shrinkage, a multidisciplinary surgical procedure was performed on August 1, 2017. This included resection of the liver metastases, cholecystectomy, peritonectomy, omentectomy, and hyperthermic intraperitoneal chemotherapy with fluorouracil, which resulted in R1 resection. Postoperative pathology confirmed metastatic adenocarcinoma in both the liver and the omentum. After surgery, the FOLFIRI regimen and bevacizumab therapy were continued for 6 cycles. In April 2019, a follow-up CT scan revealed a bladder tumor and pelvic lymph node metastasis. Cystoscopy and biopsy pathology revealed metastatic cancer of intestinal origin, and immunohistochemical testing indicated HER2+++ status (Fig. 1a, b). Fluorescence in situ hybridization (FISH) was positive. Chemotherapy and targeted therapy with capecitabine (1,500 mg after breakfast and 2,000 mg after dinner) combined with trastuzumab (400 mg) and pyrotinib (400 mg) were administered every 3 weeks from April 30, 2019, to January 10, 2021, with the best efficacy evaluated as a PR (Fig. 2). Disease progression in January 2021 prompted the initiation of therapy with trastuzumab emtansine at a dosage of 230 mg every 3 weeks. Prior to this, we performed proteomic sequencing (Shanghai Bioprofile, China) on tissue samples before and after treatment with capecitabine combined with trastuzumab and pyrotinib (Fig. 3). Tumor progression occurred again in May 2021. Two cycles of treatment with trastuzumab and pertuzumab were administered, but the disease continued to progress. Twelve cycles of treatment with irinotecan, raltitrexed, and bevacizumab were administered from August 5, 2021, to April 30, 2022. Tumor progression was detected on May 22, 2022, and treatment with disitamab vedotin was continued for 4 cycles. In August 2022, the disease progressed, and another cystoscopy examination was performed. Histopathological examination revealed intestinal-type adenocarcinoma in the bladder. The immunophenotypic profile was consistent with that of primary colorectal metastasis. Immunohistochemical staining of HER2 still revealed +++ staining (Fig. 1d). Twelve cycles of treatment with trastuzumab deruxtecan (T-DXd) were performed from October 2022 to August 2023. Unfortunately, disease progression reappeared in September 2023. Starting in September 2023, trifluridine and tipiracil hydrochloride tablets (TAS-102) combined with pyrotinib, trastuzumab, and cetuximab were administered. The treatment timeline and key clinical events of the present case are summarized in Figure 4. The progression-free survival (PFS) of patients who received various treatment regimens is shown in Table 1.

Fig. 1.

a, b HE staining and HER2 immunohistochemical staining of bladder metastases in April 2019. c, d HE staining and HER2 immunohistochemical staining of bladder metastases in August 2022.

Fig. 2.

a Abdominal CT revealed a bladder mass with thickening of the right bladder wall before the first treatment with capecitabine, trastuzumab, and pyrotinib. b After 2 cycles of treatment, the metastatic bladder tumor shrank. c After 4 cycles of treatment, the tumor further shrank and achieved a PR. d After 20 months of treatment, the tumor grew again and was evaluated as progressive disease.

Fig. 3.

a Generation of a heatmap illustrating differential protein changes. b GO analysis of differential protein changes. c The top 10 protein associated with biological process (BP) terms in the GO analysis. d The top 10 protein associated with cellular component (CC) terms in the GO analysis. e The top 10 protein associated with molecular function (MF) terms in the GO analysis. f KEGG pathway analysis of the differential proteins changes. g Protein-protein interaction network (PFIN) based on differential protein changes.

Fig. 4.

Treatment timeline and key clinical events of the present case.

Table 1.

The PFS of patients who received various treatment regimens

Treatment lines	Treatment regimen	PFS
Perioperative treatment	mFOLFOX+cetuximab	24 months
First line	FOLFIRI+bevacizumab	29 months
Second line	Capecitabine+trastuzumab+pyrotinib	20 months
Third line	Trastuzumab emtansine	4 months
Fourth line	Trastuzumab+pertuzumab	2 months
Fifth line	Irinotecan+raltitrexed+bevacizumab	9 months
Sixth line	Disitamab vedotin	3 months
Seventh line	T-DXd	10 months
Eighth line	TAS-102+trastuzumab+pyrotinib+cetuximab	9 months

Discussion

Human epidermal growth factor receptor 2, also known as HER2 protein, is a transmembrane glycoprotein with tyrosine kinase activity that is encoded by the oncogene HER2/neu [8]. HER2 drives tumor cell differentiation, proliferation, infiltration, and metastasis. As an important target of antitumor therapy, HER2 has been successfully used to treat breast and advanced gastric cancers, significantly improving patient prognosis and survival [9–11]. The mutation rate of HER2 in advanced CRC is approximately 2–3%, and it mostly occurs in RAS/BRAF wild-type left colon and rectal cancer [12, 13].

In current clinical practice for CRC, significant heterogeneity exists across institutions in the platforms and scoring criteria for HER2 testing. This variability extends to clinical trials, where classic studies such as DESTINY-CRC02 [14], DESTINY-PanTumor02 [15], MOUNTAINEER [16], and MOUNTAINEER-03 [17] have adopted the gastric cancer HER2 criteria (IHC 3+ in >10% of tumor cells), while the HERACLES and HERACLES-B trials employed the more stringent HERACLES criteria [18, 19]. The latest NCCN guidelines (2025.v4 for colon cancer and 2025.v2 for rectal cancer) recommend HER2 testing for patients with suspected or confirmed metastatic disease using IHC and FISH. These guidelines endorse the HERACLES criteria for defining HER2 positivity: IHC 3+ in >50% of tumor cells. Cases with an IHC score of 2+ should be reflexively tested by FISH, with positivity defined as a HER2/CEP17 ratio ≥2.0 in >50% of cells [18]. HER2 amplification detected by NGS is also considered positive. This standardized criterion is notably more stringent than the established HER2 positivity standards for gastric and breast cancers. An in-depth understanding of HER2-positive CRC has created a pressing need for standardized diagnostic criteria, which will serve as a cornerstone for future research and clinical practice.

Activation of the HER2 signaling pathway can circumvent EGFR inhibition by engaging downstream signaling bypass pathways (such as the PI3K-AKT-mTOR and MAPK pathways) [20]. This sustained signaling promotes continued tumor cell proliferation and survival, thereby decreasing the efficacy of anti-EGFR therapies. HER2 mutation is believed to indicate resistance to EGFR-targeted drugs in CRC [5, 21]. Early preclinical studies on subcutaneous transplant tumors have demonstrated the efficacy of anti-HER2 therapy in HER2-positive CRC, with dual-target therapy showing better efficacy than anti-HER2 single-target therapy [22, 23]. HERACLES is the first clinical study of anti-HER2 dual-target therapy using trastuzumab combined with lapatinib in treatment-refractory, HER2-positive mCRC with wild-type KRAS codon 12/13; the objective response rate (ORR) was 30%, and the disease control rate was 74% [18]. The MyPathway basket trial (phase IIA) included a cohort investigating dual HER2 blockade with trastuzumab plus pertuzumab in patients with HER2-amplified mCRC. Among 43 HER2-positive, RAS wild-type patients, the ORR was 40%, with a median PFS of 5.3 months and a median overall survival (OS) of 14 months [24]. The MOUNTAINEER study revealed that the ORR for CRC patients receiving trastuzumab combined with tucatinib was 38.1%, with a median PFS of 8.2 months and a median OS of 24.1 months [16]. Moreover, compared with tucatinib alone, the combination of trastuzumab and tucatinib resulted in greater antitumor activity. MOUNTAINEER-03 is a phase III study evaluating mFOLFOX6 in combination with tucatinib and trastuzumab as first-line treatment for HER2-positive mCRC, and the trial is currently ongoing. Another small-molecule tyrosine kinase inhibitor, pyrotinib, is a second-generation, irreversible, well-absorbed pan-ErbB receptor tyrosine kinase inhibitor that targets HER1, HER2, and HER4 [25]; it has been granted by the National Medical Products Administration (NMPA) of China for HER2-positive breast cancer. A phase II study revealed that the PFS of patients treated with pyrotinib with or without trastuzumab for treatment-refractory, HER2-positive mCRC was 5.7 months, and the PFS of patients in the pyrotinib plus trastuzumab subgroup reached 8.6 months [26]. The phase II DESTINY-CRC01 trial evaluated T-DXd (6.4 mg/kg) in HER2-positive, RAS wild-type mCRC patients who had progressed on two or more prior regimens. In patients with HER2 IHC 3+ or IHC 2+/ISH+ disease, T-DXd demonstrated an ORR of 45.3%, a median PFS of 6.9 months, and a median OS of 15.5 months; however, this was accompanied by a considerable incidence of treatment-related adverse events [27]. In the DESTINY-CRC02 study, a reduced dose of T-DXd (5.4 mg/kg) was established as a viable option, demonstrating comparable antitumor activity to the standard 6.4 mg/kg dose but with a more favorable safety profile in patients with HER2-positive mCRC [14]. According to the phase II studies mentioned above, dual-target HER2 therapy is an effective measure for refractory HER2-positive mCRC. To date, no randomized controlled phase III studies have substantiated this conclusion. The paucity of research on the combination of chemotherapy and anti-HER2 targeting agents leaves the potential for enhanced efficacy through dual-targeted therapy unexplored.

The current case suggests that combining chemotherapy with dual HER2 blockade merits further investigation as a therapeutic strategy for HER2-positive mCRC. The patient initially received perioperative therapy with an oxaliplatin-based regimen plus an anti-EGFR agent. This was subsequently followed by a first-line irinotecan-based regimen combined with anti-VEGF therapy for metastatic disease. Upon recurrence, bladder metastasis was identified. Pathological examination confirmed metastatic colon cancer, which was HER2-positive (IHC 3+). The combination therapy of capecitabine, trastuzumab, and pyrotinib achieved a PR, with a median PFS of 20 months. Compared with other HER2-targeted therapies, this regimen resulted in significantly longer PFS in mCRC patients. We hypothesize that this clinical superiority may be attributable to a synergistic effect achieved by combining HER2 blockade with a capecitabine-based chemotherapy backbone. However, whether combination chemotherapy outperforms targeted therapy alone remains unclear and warrants further investigation. Unlike in breast and gastric cancers, HER2 positivity in CRC is relatively rare, and treatment options have historically remained limited and underrecognized. The field currently lacks large-scale phase III trial data, and anti-HER2 therapies have not yet received regulatory approval for CRC in China. However, with the increasing adoption of precision medicine and the emergence of new clinical evidence, the therapeutic landscape for HER2-positive CRC is undergoing a paradigm shift toward standardization and diversification. The successive introduction of novel anti-HER2 agents, which demonstrate continuously improving efficacy and survival outcomes, is poised to expand the treatment arsenal for this patient population. This case suggests that dual HER2-targeted therapy combined with chemotherapy is a promising strategy for HER2-positive mCRC patients with good performance status. This approach warrants validation in large-scale clinical trials to confirm its efficacy and ultimately guide clinical decision-making, particularly in patients with a good performance status.

To investigate the molecular mechanisms of resistance, we performed proteomic sequencing following disease progression on a regimen of capecitabine combined with trastuzumab and pyrotinib. This analysis revealed 2,161 upregulated and 1,110 downregulated proteins. Gene Ontology (GO) analysis revealed that these differentially expressed proteins were involved in diverse biological processes. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG)-based functional enrichment analysis revealed that the most significantly enriched pathways were metabolic pathways and complement and coagulation cascades. Subsequent research should validate the functional significance of these candidate genes and pathways, with the goal of identifying novel therapeutic targets for overcoming resistance.

Conclusion

HER2 testing is indispensable in mCRC, particularly in the context of wild-type RAS disease. As research advances, establishing a consensus HER2 scoring criterion is imperative. Anti-HER2 therapy has demonstrated a survival benefit in HER2-positive mCRC patients previously treated with oxaliplatin, irinotecan, and fluorouracil. For those with good performance status, a combination of dual HER2-targeted therapy and chemotherapy represents a promising strategy, the efficacy of which awaits validation in future phase III clinical trials. Furthermore, a critical area of ongoing research involves elucidating the mechanisms of resistance, including the identification of associated genetic and proteomic alterations.

Acknowledgment

We thank Bingjing Jiang, a pathologist in the pathology department of Affiliated Jinhua Hospital, Zhejiang University School of Medicine, for her assistance in pathologic diagnosis.

Statement of Ethics

The case report received approval from the Ethics Committee of Jinhua Hospital of Zhejiang University School of Medicine (approval No. GA200503). Written informed consent for publication was obtained from all participants. Patient’s informed consent has been obtained. The CARE Checklist has been completed by the authors for this case report, attached as online supplementary material (for all online suppl. material, see https://doi.org/10.1159/000549570).

Conflict of Interest Statement

The authors have no conflicts of interest to declare.

Funding Sources

This study was supported by grants from Affiliated Jinhua Hospital, Zhejiang University School of Medicine (Grant No. JY2020-2-04, JY2021-1-05). And this work was also supported by the Jinhua Science and Technology Programs (2022-4-086, 2023-4-070).

Author Contributions

Practical performance: Wanfen Tang, Hongjuan Zheng, Qinghua Wang, and Xia Zhang. Investigation: Wanfen Tang, Hongjuan Zheng, and Shishi Zhou. Image analysis: Chenyang Ge. Funding acquisition: Wanfen Tang and Hongjuan Zheng. Preparation of the manuscript: Wanfen Tang. Conceptualization and project administration: Jianfei Fu.

Funding Statement

This study was supported by grants from Affiliated Jinhua Hospital, Zhejiang University School of Medicine (Grant No. JY2020-2-04, JY2021-1-05). And this work was also supported by the Jinhua Science and Technology Programs (2022-4-086, 2023-4-070).

Data Availability Statement

The data that support the findings of this study are not publicly available due to their containing information that could compromise the privacy of research participants but are available from the corresponding author, Jianfei Fu (11218276@zju.edu.cn), upon reasonable request.