The most common metastatic sites of breast carcinoma are the local and distant lymph nodes, bone, lung, liver and brain. Breast carcinoma metastases to the gastrointestinal tract as first metastatic site are extremely rare. However, according to a report on breast cancer metastases to the stomach in autopsy cases, it was found in 2 to 18% of cases [2
]. On the other hand, according to a report of clinical cases by Taal et al. [3
], the morbidity rate of breast cancer metastasis to the stomach is approximately 0.3%. It is believed that this difference may be due to underestimation because the symptoms of breast cancer metastases to the stomach were nonspecific, including indigestion, lack of appetite, and epigastric pain, and, therefore, no close examination such as by endoscope was performed unless serious symptoms were observed, resulting in metastases being overlooked [3
]. Furthermore, there are some reasons that make diagnosis difficult. The endoscopic finding of a typical gastric metastasis is diffuse intramural infiltration imitating linitis plastica, 50% of which involves mucosal abnormalities that are difficult to differentiate as normal or benign. As a result, many cases are not diagnosed as breast cancer metastasis to the stomach until surgery is performed. Furthermore, because tumors are located in deep mucosal tissue, it is not rare for a biopsy to show a false negative [3
]. Therefore, in the past, there have not been any studies on diagnostic performance for gastric metastasis using endoscopic ultrasound, but this method may be useful in making a morphological diagnosis and selecting an appropriate biopsy location [8
For an accurate differential diagnosis between primary gastric cancer and breast cancer metastasis to the stomach, immunostaining methods are recommended. Van Velthuysen et al. [9
] reported that second-generation estrogen receptors are not observed in the expression of gastric cancer and are useful in diagnosing breast cancer metastases to the stomach. However, when estrogen receptors of the primary lesion are negative, as in the present case, they are not useful. GCDFP-15 is a substance found in breast cysts and the plasma of patients with breast carcinoma, and antibodies of this may be useful for accurately diagnosing whether a metastatic tumor is primary breast carcinoma. According to some reports, their sensitivity is 55-76% and their specificity is 95-100% [10
]. It has been reported that the immunostaining of CK7 and 20 is also useful for making a differential diagnosis in order to distinguish this case from gastric cancer [11
The present case is of a breast ductal carcinoma metastasis to the stomach, but it has been reported that breast carcinoma metastases to the gastrointestinal tract are frequently observed in lobular carcinoma. Lobular breast carcinoma frequently takes the form of a signet ring and may be confused with primary gastric signet ring cells [3
According to a case series of 73 patients by McLemore et al. [13
], the median survival period was 28 months, and anticancer agents and hormone treatment were effective, but surgery did not improve the prognosis. Therefore, treatment should be limited to palliative bypass for obstruction to the passage due to gastric obstruction.
In conclusion, when a patient with a previous history of breast carcinoma complains of digestive symptoms or is diagnosed as having primary gastric cancer, it is necessary to consider the possibility of breast cancer metastasis to the stomach. For a differential diagnosis, immunostaining is recommended, and when a diagnosis of breast cancer metastasis to the stomach is made, systemic therapy is necessary.