A Rare Case of Triple-Positive Breast Cancer With Eventual Triple-Negative Small Bowel Metastasis

Invasive lobular breast cancer (ILBC) is a common cause of breast cancer. Prognosis is dependent on many factors such as metastasis location and hormone receptor positivity. A 59-year-old postmenopausal African-American female who was referred to our clinic in May of 2022 presented with a suspicious small bowel lesion seen on surveillance imaging. The patient was diagnosed 15 years prior, with hormone receptor triple positive ILBC of the left breast, T1N2M0. In March of 2021, the patient was admitted to the hospital for rectal bleeding and was also found to have an elevated carcinoembryonic antigen (CEA) level. Computed tomography of the abdomen and pelvis was performed, which revealed a 4 cm segment of proximal ileum that was indeterminate for inflammation, neoplasm, or focal ischemia. The patient ultimately agreed to proceed with a diagnostic laparoscopy to further identify this area and underwent a small bowel resection. The final pathology of this specimen revealed a poorly differentiated, diffuse-type carcinoma with a focal mucinous matrix. The tumor involved the submucosa, serosa, and pericolonic adipose tissue. The morphology was consistent with metastatic carcinoma originating from ILBC. The hormone receptors for this specimen revealed estrogen-receptor (ER) negative, progesterone-receptor (PR) negative, and human epidermal growth factor receptor-2 (HER-2) negative. Lobular breast cancer metastasis to the small bowel as well as triple positive to triple negative conversion is exceedingly rare. The recurrence and metastasis of breast cancer are considerably high and the survival rate for these individuals has shown little improvement throughout the last decade. Defining relevant prognostic markers is crucial for improved management with known metastasis and triple negative receptors.