Response to Third-Line Erlotinib in Peritoneal Carcinomatosis from Initially EGFR Mutation-Negative Lung Adenocarcinoma, Followed by the Retrospective Confirmation of EGFR Mutation-Positivity by Immunohistochemistry

Q: What is the clinical evidence from this study?

Study design: Case Report. Population: Advanced lung adenocarcinoma with peritoneal carcinomatosis (n=1). Intervention: Erlotinib. Primary outcome: Improvement in performance status and reduction in peritoneal carcinomatosis.

Q: What does this research mean for the field?

Initial single-plex EGFR testing in lung adenocarcinoma can yield false-negative results, meaning some patients initially diagnosed as EGFR mutation-negative may still harbor mutations and benefit from EGFR-targeted therapies like erlotinib. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

Yuki Fujimoto; Takashi Inao; Miki Ikeuchi; Akiko Shimizu; Chiho Ohbayashi; Asuka MITSUI; Mai Imao; Kohei Namba; Sachie Kume; Kazuya Monden; Kojiro Otsuka; Yujiro Suzuki

doi:10.2169/internalmedicine.7216-26

January 1, 2026Internal MedicineOpen Access

Response to Third-Line Erlotinib in Peritoneal Carcinomatosis from Initially EGFR Mutation-Negative Lung Adenocarcinoma, Followed by the Retrospective Confirmation of EGFR Mutation-Positivity by Immunohistochemistry

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Key result

Third-line erlotinib linked to improved performance status and reduced peritoneal carcinomatosis lasting 9 months.

n=1

Why the study?

Does erlotinib improve outcomes in patients with peritoneal carcinomatosis from initially EGFR mutation-negative lung adenocarcinoma?

Key Points

This report aims to illustrate the clinical response to third-line erlotinib in a patient with previously confirmed EGFR mutation-negative lung adenocarcinoma.
Case report of a woman in her late 50s with advanced lung adenocarcinoma.
Treated with cytotoxic chemotherapy, immune checkpoint inhibitors, and third-line erlotinib.
Immunohistochemistry of ascitic fluid was performed to confirm EGFR mutation status.
Performance status improved from 3 to 2 within 10 days of starting erlotinib.
Marked reduction in peritoneal carcinomatosis observed after 4 months of treatment.
EGFR L858R mutation identified through immunohistochemistry in ascitic fluid.

Study Design

Type

Case Report (n=1)

Structured PICO

Does erlotinib improve outcomes in patients with peritoneal carcinomatosis from initially EGFR mutation-negative lung adenocarcinoma?

P

Population

1 woman in her late 50s with advanced lung adenocarcinoma (cTXN0M1a, stage IVA) and peritoneal carcinomatosis, initially EGFR mutation-negative on single-plex testing.

I

Intervention

Erlotinib 150 mg/day oral as third-line therapy.

O

Outcome

Improvement in performance status and reduction in peritoneal carcinomatosis.surrogate

Erlotinib may provide significant clinical benefit in patients with lung adenocarcinoma and peritoneal carcinomatosis who are subsequently found to have EGFR mutations by immunohistochemistry, despite initial negative molecular testing.

Limitations

Possibility of acquiring an EGFR mutation during the clinical course cannot be completely excluded
Additional molecular testing could not be performed because of the limited amount of residual material in the initial pleural biopsy specimens

Implication

May warrant IHC retesting for EGFR in peritoneal carcinomatosis from lung adenocarcinoma; hypothesis-generating for erlotinib benefit.

Abstract

A woman in her late 50s with advanced lung adenocarcinoma, initially EGFR mutation-negative on single-plex testing, received cytotoxic chemotherapy and immune checkpoint inhibitors. After 1 year and 8 months, she developed peritoneal carcinomatosis. Third-line erlotinib led to an improvement in her performance status (PS 3 to 2 in 10 days) and a marked reduction in peritoneal carcinomatosis after 4 months, with the effect lasting for 9 months. Immunohistochemistry of the ascitic fluid revealed an EGFR L858R mutation. This case highlights the possibility of false-negative results on initial testing and suggests the potential benefit of EGFR-TKIs, even in EGFR mutation-negative cases at diagnosis.

Discussion

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Cite This Study

Fujimoto et al. (2026) conducted a case report in Advanced lung adenocarcinoma with peritoneal carcinomatosis (n=1). Erlotinib was evaluated on Improvement in performance status and reduction in peritoneal carcinomatosis. Third-line erlotinib led to an improvement in performance status from 3 to 2 in 10 days and a marked reduction in peritoneal carcinomatosis lasting 9 months.

synapsesocial.com/papers/6a13e6ee0e02ee3982d31af3 https://doi.org/10.2169/internalmedicine.7216-26

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Response to Third-Line Erlotinib in Peritoneal Carcinomatosis from Initially EGFR Mutation-Negative Lung Adenocarcinoma, Followed by the Retrospective Confirmation of EGFR Mutation-Positivity by Immunohistochemistry

Key Points

Study Design

Structured PICO

Limitations

Implication

Abstract

Discussion

Cite This Study

Response to Third-Line Erlotinib in Peritoneal Carcinomatosis from Initially EGFR Mutation-Negative Lung Adenocarcinoma, Followed by the Retrospective Confirmation of EGFR Mutation-Positivity by Immunohistochemistry

Key Points

Study Design

Structured PICO

Limitations

Implication

Abstract

Discussion

Cite This Study

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