# Gastric Signet Ring Cell Carcinoma Metastasis From Lobular Breast Cancer: A Diagnostic Pitfall

## TL;DR

A rare case of breast cancer metastasizing to the stomach is described, highlighting the need for careful diagnosis to distinguish it from primary stomach cancer.

## Contribution

The paper presents a unique case of metastasis from lobular breast cancer to the stomach with signet ring cell features.

## Key findings

- The gastric lesion was confirmed as a metastasis from the patient's prior lobular breast cancer.
- Immunohistochemistry was crucial in differentiating the metastasis from primary gastric cancer.
- The case emphasizes the importance of considering metastasis in diagnosing gastric signet ring cell carcinoma.

## Abstract

Breast cancer is the most common type of cancer among women worldwide. Gastric metastasis from invasive lobular carcinoma of the breast is unusual.

We report the case of a 66-year-old woman, under follow-up for an invasive classic lobular carcinoma of the left breast treated four years prior, who was admitted for upper abdominal discomfort and worsening constipation. Linitis plastica was suspected at gastroscopy.

Histology of gastric biopsies showed a poorly cohesive carcinoma comprising signet ring cells, with no resemblance to the original breast cancer. An adequate immunochemistry panel, including estrogen receptor and GATA-3, eliminated primary gastric cancer and proved that the gastric lesion was a metastasis of the previously diagnosed invasive lobular breast cancer with additional signet ring cell differentiation, which is classified among its rare variants.

This challenging case shows the importance of oncologic medical history and immunochemistry in differentiating between metastasis from invasive lobular breast carcinoma and primary gastric cancer. The distinction is necessary as the prognosis and approaches for treatment are different.

When encountering a gastric signet ring cell carcinoma, one must keep in mind that it actually can be a metastasis from one of the several primary sites of origin.