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Case Report Open Access

Post‑operative liver metastasis from gastric cancer with HER2‑positive areas newly identified upon re‑evaluation, leading to a favorable response to trastuzumab‑based therapy: A case report

  • Authors:
    • Shinsuke Usui
    • Kenichi Iwasaki
    • Ryota Sakon
    • Ryuichi Wada
    • Tatsushi Suwa
  • View Affiliations / Copyright

    Affiliations: Department of Surgery, Kashiwa Kousei General Hospital, Kashiwa, Chiba 277‑8551, Japan, Department of Diagnostic Pathology, Kashiwa Kousei General Hospital, Kashiwa, Chiba 277‑8551, Japan
    Copyright: © Usui et al. This is an open access article distributed under the terms of Creative Commons Attribution License [CC BY 4.0].
  • Article Number: 43
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    Published online on: June 11, 2026
       https://doi.org/10.3892/mi.2026.327
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Abstract

Recent advances in molecular targeted agents and immune checkpoint inhibitors have markedly improved outcomes in patients with unresectable or recurrent advanced‑stage gastric cancer. As treatment options continue to expand, biomarker testing has become essential for determining first‑line treatment strategies. Among these, human epidermal growth factor receptor 2 (HER2) plays a key role in treatment selection; however, the intratumoral heterogeneity of HER2 expression in gastric cancer has long been recognized and may influence therapeutic decision‑making. The present study describes the case of a patient who was initially diagnosed as having a HER2 score of 0 on the surgical specimen, but was later found to have a HER2 score of 2+ with FISH positivity upon reassessment, subsequently demonstrating a favorable response to trastuzumab‑based therapy. The patient was a 79‑year‑old man with a type 3 lesion at the cardia, and enlarged lymph nodes adjacent to the primary tumor. The pre‑operative diagnosis was cT4aN1M0, stage III. He underwent total gastrectomy. At 27 months post‑surgery, MRI revealed a 21‑mm metastatic lesion in liver segment 8. Given the initial HER2 score of 0, nivolumab plus the oxaliplatin + leucovorin + 5‑fluorouracil regimen (mFOLFOX6) was initiated as first‑line systemic therapy. However, as tumor markers continued to increase after two cycles, HER2 was re‑evaluated using a different section from the resected specimen, which revealed a score of 2+ with FISH positivity. Therefore, the treatment was switched to trastuzumab plus mFOLFOX6. Following the regimen change, tumor markers decreased, and a CT scan demonstrated the shrinkage of the liver metastasis to 13 mm. Chemotherapy remains ongoing 7 months following the initiation trastuzumab treatment. On the whole, the present case report suggests that the reassessment of HER2 status may help identify patients who may benefit from HER2‑targeted therapy, and may ultimately improve the therapeutic efficacy of chemotherapy. 
View Figures

Figure 1

Upper gastrointestinal endoscopic
findings, macroscopic finding of the resected stomach and
pathological findings, and contrast-enhanced CT scan prior to
surgery. (A) Upper gastrointestinal endoscopy illustrating a type 3
lesion at the cardia, accompanied by minimal esophageal
involvement. (B) Contrast enhanced abdominal CT scan illustrating
gastric wall thickening with central depression at the cardia and
multiple enlarged lymph nodes adjacent to the primary tumor, which
are highlighted within the yellow circle. (C) Macroscopic
examination of the resected stomach demonstrating a type 3 tumor
measuring 60x50 mm, and histopathological analysis revealed well-
to moderately differentiated tubular adenocarcinoma, classified as
pT3, pN2 (4/60), Ly1b, V1a, with negative proximal and distal
margins (pPM0, pDM0). The biomarker analysis showed HER2 score of
0, pMMR, CLDN18.2-negative, and PD-L1 (28-8) CPS >5, as
described in the text. CT, computed tomography.

Figure 2

Contrast-enhanced CT scan at 25 months
post-operatively, MRI at 27 months post-operatively, and
contrast-enhanced CT scan at 31 months post-operatively (following
four cycles of trastuzumab plus mFOLFOX6). The white triangles
indicate the location of the tumor. (A) Contrast-enhanced CT scan
at 25 months post-operatively illustrating a faint 15-mm
low-density area in segment 8 of the liver. (B) MRI at 27 months
demonstrating a 21x19-mm round lesion in segment 8 of the liver,
showing low signal intensity on T1-weighted imaging and mildly high
signal on T2-weighted imaging, consistent with liver metastasis
from gastric cancer and demonstrated a continued tendency to
enlarge. (C) Contrast-enhanced CT scan at 31 months demonstrating
shrinkage of the segment 8 liver metastasis to 13 mm. CT, computed
tomography.

Figure 3

The resected stomach and
immunohistochemistry of HER2. (A) The location of the section for
the initial examination (No. 1) and for re-evaluation (No. 2). (B)
Histological analysis and immunohistochemistry of HER2 at the
initial examination. HER2 was not observed in well-differentiated
adenocarcinoma (hematoxylin and eosin staining and
immunohistochemistry of HER2; magnification, x100). (C)
Histological analysis and immunohistochemistry of HER2 at the
re-evaluation. Moderate membranous expression of HER2 (score 2+)
was noted in the well differentiated adenocarcinoma (hematoxylin
and eosin staining and immunohistochemistry of HER2; magnification,
x100).

Figure 4

Graph depicting the clinical course of
the patient from the onset of liver metastasis through the
initiation of chemotherapy, as demonstrated by changes in tumor
markers (CEA and CA19-9). The timing of imaging examinations
presented in Fig. 2 is also
indicated. CEA, carcinoembryonic antigen; CA19-9, carbohydrate
antigen 19-9; CT, computed tomography; POM, post-operative month;
Nivo, nivolumab; mFOLFOX6, oxaliplatin + leucovorin +
5-fluorouracil regimen; Tmab, trastuzumab.
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Copy and paste a formatted citation
Spandidos Publications style
Usui S, Iwasaki K, Sakon R, Wada R and Suwa T: Post‑operative liver metastasis from gastric cancer with HER2‑positive areas newly identified upon re‑evaluation, leading to a favorable response to trastuzumab‑based therapy: A case report. Med Int 6: 43, 2026.
APA
Usui, S., Iwasaki, K., Sakon, R., Wada, R., & Suwa, T. (2026). Post‑operative liver metastasis from gastric cancer with HER2‑positive areas newly identified upon re‑evaluation, leading to a favorable response to trastuzumab‑based therapy: A case report. Medicine International, 6, 43. https://doi.org/10.3892/mi.2026.327
MLA
Usui, S., Iwasaki, K., Sakon, R., Wada, R., Suwa, T."Post‑operative liver metastasis from gastric cancer with HER2‑positive areas newly identified upon re‑evaluation, leading to a favorable response to trastuzumab‑based therapy: A case report". Medicine International 6.4 (2026): 43.
Chicago
Usui, S., Iwasaki, K., Sakon, R., Wada, R., Suwa, T."Post‑operative liver metastasis from gastric cancer with HER2‑positive areas newly identified upon re‑evaluation, leading to a favorable response to trastuzumab‑based therapy: A case report". Medicine International 6, no. 4 (2026): 43. https://doi.org/10.3892/mi.2026.327
Copy and paste a formatted citation
x
Spandidos Publications style
Usui S, Iwasaki K, Sakon R, Wada R and Suwa T: Post‑operative liver metastasis from gastric cancer with HER2‑positive areas newly identified upon re‑evaluation, leading to a favorable response to trastuzumab‑based therapy: A case report. Med Int 6: 43, 2026.
APA
Usui, S., Iwasaki, K., Sakon, R., Wada, R., & Suwa, T. (2026). Post‑operative liver metastasis from gastric cancer with HER2‑positive areas newly identified upon re‑evaluation, leading to a favorable response to trastuzumab‑based therapy: A case report. Medicine International, 6, 43. https://doi.org/10.3892/mi.2026.327
MLA
Usui, S., Iwasaki, K., Sakon, R., Wada, R., Suwa, T."Post‑operative liver metastasis from gastric cancer with HER2‑positive areas newly identified upon re‑evaluation, leading to a favorable response to trastuzumab‑based therapy: A case report". Medicine International 6.4 (2026): 43.
Chicago
Usui, S., Iwasaki, K., Sakon, R., Wada, R., Suwa, T."Post‑operative liver metastasis from gastric cancer with HER2‑positive areas newly identified upon re‑evaluation, leading to a favorable response to trastuzumab‑based therapy: A case report". Medicine International 6, no. 4 (2026): 43. https://doi.org/10.3892/mi.2026.327
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