A 52-year-old female patient applied to our clinic due to a rapidly growing palpable breast mass. She had no history of breast cancer in her family. She had subtotal distal gastrectomy and cytoreductive surgery due to signet-cell gastric carcinoma with intraabdominal lymph node, peritoneal and ovarian metastases 18 months ago. She developed bone metastases in the L3 vertebra and left iliac bone 6 months after the operation.
Her ultrasound examination showed a subcutaneous mass of 1 cm in diameter in the upper inner quadrant of the left breast (Fig. 1a). The mass was heterogeneous in echotexture and irregular in shape accompanied by peritumoral echogenicity. It was vertically oriented and had spiculated margins without any posterior acoustic features. Colour Doppler imaging of the lesion displayed high peripheral and central vascularity (Fig. 1b). The tissue elasticity of lesion was 179 kPa and hard with shear wave elastography (Fig. 1c).
The lesion was hardly seen on the mammogram due to the relatively low density of the mass, which was of the same density as the breast parenchyma. However, the lesion was delineated on the craniocaudal view as a focal asymmetry (Fig. 2a), which was also obscure in spot magnified image (Fig. 2b). It however presented as a round mass with fine spiculations on the MLO view (Fig. 2c) and tomosynthesis image (Fig. 2d).
The incidence of metastasis to the breast from any primary tumour is around 0.2–1.3% . Accordingly, it has been reported that only less than 0.3% of gastric cancer patients developed breast metastasis . Metastasis of signet-ring cell gastric carcinoma to the breast is very rare and to our knowledge, there are less than 50 reported cases in the PubMed database [1,2,3,4,8].
Differentiating primary and secondary breast cancers is highly important as the management differs. However, it has been shown that metastatic tumours in the breast have a wide range of appearances. Imaging findings may vary depending on the route of dissemination of the disease [5,6,7]. Haematogenous metastases present as single or multiple, round to oval shaped, circumscribed masses commonly located superficially in the subcutaneous tissue or adjacent to the breast parenchyma that has relatively rich blood supply [5,7]. Unlike the primary tumours of the breast; spiculations, calcification, skin changes or architectural distortion are not seen in haematogenous breast metastases . They tend to grow rapidly and lack desmoplastic response which is a typical finding of primary breast cancer. On the other hand, tumours which disseminate via lymphatic route probably present with diffuse breast oedema, lymph node enlargement and skin thickening associating with a thick trabecular pattern mimicking the inflammatory cancer of the breast.
Iesato et al evaluated 41 cases of gastric cancer metastases to the breast . Among the cases that had imaging data, they found that mammographic findings of these breast metastases included well-circumscribed nodules or skin thickening. In the ultrasound examination, the lesions appeared as irregularly shaped hypoechoic nodules, diffuse hypoechoic lesions or skin thickening. Some of the cases could not be visualised by mammography or ultrasound. Clinical findings such as skin changes and breast enlargement conveyed to further evaluate these cases with biopsy. In our case, the density of the lesion was similar to the breast parenchyma which caused masking. It could be differentiated from the breast tissue due to fine spiculations, which is not defined in metastatic gastric carcinomas to the breast.
In a patient with a history of gastric carcinoma, a breast lesion particularly recently found or rapidly growing, should be scrutinised for the possibility of metastasis, even if it has similar radiological findings as primary breast cancer.
US-guided core needle biopsy of the lesion revealed signet-cell metastasis of the primary stomach cancer to the breast in the histopathologic examination, showing similar tissue characteristics as the primary gastric tumour. The patient developed bilateral pleural effusion and mediastinal lymphadenopathy. Pleural biopsies revealed bilateral pleural metastases. The patient deceased one month after the diagnosis of breast metastasis.
Written informed patient consent for publication has been obtained.
 Alvarado Cabrero I, Carrera Alvarez M, Perez Montiel D, Tavassoli FA. Metastases to the breast. Eur J Surg Oncol. England; 2003 Dec;29(10):854–5. (PMID: 14624777)
 Yan H, Liu J, Ming X, Zhou X, Jin H, Li X, et al. Metastatic gastric carcinoma to the breast: A case report and review of the Chinese literature. Mol Clin Oncol. England; 2017 Aug;7(2):221–4. (PMID: 28781789)
 He C-L, Chen P, Xia B-L, Xiao Q, Cai F-L. Breast metastasis of gastric signet-ring cell carcinoma: a case report and literature review. World J Surg Oncol. England; 2015 Mar;13:120. (PMID: 25890325)
 Sato T, Muto I, Fushiki M, Hasegawa M, Hasegawa M, Sakai T, et al. Metastatic breast cancer from gastric and ovarian cancer, mimicking inflammatory breast cancer: report of two cases. Breast Cancer. Japan; 2008;15(4):315–20. (PMID: 18311479)
 Mun SH, Ko EY, Han B-K, Shin JH, Kim SJ, Cho EY. Breast metastases from extramammary malignancies: typical and atypical ultrasound features. Korean J Radiol. Korea (South); 2014;15(1):20–8. (PMID: 24497788)
 Lee JH, Kim SH, Kang BJ, Cha ES, Kim HS, Choi JJ. Metastases to the breast from extramammary malignancies-sonographic features. J Clin Ultrasound. United States; 2011 Jun;39(5):248–55. (PMID: 21469153)
 Lee SH, Park JM, Kook SH, Han BK, Moon WK. Metastatic tumors to the breast: mammographic and ultrasonographic findings. J Ultrasound Med. England; 2000 Apr;19(4):257–62. (PMID: 10759349)
 Iesato A, Oba T, Ono M, Hanamura T, Watanabe T, Ito T, et al. Breast metastases of gastric signet-ring cell carcinoma: a report of two cases and review of the literature. Onco Targets Ther. New Zealand; 2015;8:91–7. (PMID: 25565869)