When these findings are considered alongside the immunohistochemical profile of the patient’s primary breast cancer in 2014—estrogen receptor positive in 50%, progesterone receptor positive in 80%, HER2 2+, Ki-67 5%, CK positive, p53 3%, and cytoplasmic p120 positive—it can be inferred that the rectal lesions are consistent with metastatic breast cancer, while the gastric lesions are associated with metastatic lobular carcinoma, supporting the diagnosis of secondary breast cancer. Here, ESR1 is linked to breast cancer.