The patient received postoperative radiotherapy and hormonal therapy (tamoxifen). Four years later, some new right axillary lymph node metastases were discovered at physical examination and therefore removed. The histological examination confirmed the diagnosis of lymphatic metastasis from ILC. Two months after lymphadenectomy, the patient presented with tenesmus and a painful anal polypoid lesion (Figure ​(Figure1).1). The mass was removed for biopsy. The immunohistochemical staining was similar to primary breast tumor [95% ER and 10% progesterone receptor (PR)], which suggested a breast origin (Figure ​(Figure2).2). Mib1 was 25% positive, while c-erbB2 was negative. No other site of disease was found by abdominal CT and bone scintigraphy. Radiotherapy was chosen for this patient, which led to complete regression of the lesion, but later an anal stenosis appeared without any changes in defecation. Treatment with anastrozole was then started. At follow-up, there was no evidence of progressive disease for 2 years, after which the level of CA15.3 began to increase, and some new right axillary lymph nodes metastases appeared. The patient underwent axillary lymphadenectomy and adjuvant hormonal therapy was continued.

Despite their rare clinical manifestations (only 0.07% of cases)[³], some necroscopy studies have described an incidence rate of colon involvement that varies from 3% to 18%[^4,5]. The risk of a second primary tumor following breast cancer is about 12%[⁶], and the incidence of metachronous primary colorectal cancer is estimated to be about 1%[^7,8]. In a review of the literature, we found 15 cases of solitary rectal metastasis from breast carcinoma, but only one case of anal localization has been reported[⁹] and none from lobular breast carcinoma. Breast ILC is responsible for the majority of metastases in the GI tract, with a metastasis rate of 4.5% vs 0.2% from infiltrating ductal carcinoma[¹⁰].

Clinical-histological features that lead us to suspect a diagnosis of gastrointestinal breast metastasis versus primary colon cancer are: (1) ER or PR protein and gross cystic disease fluid protein (GCDFP-15) are strongly positive in metastatic breast carcinomas[^10–12]; (2) absence of dysplasia in adjacent colonic epithelium suggests a metastatic growth; and (3) history of breast cancer. However, some authors have shown the presence of cells positive for ER or PR in colorectal cancer, but their concentration tends to be lower than in breast cancer[^13,14]. In our case, GCDFP-15 was not tested for, but the immunohistochemical staining of anal biopsy was strongly positive for ERs (90%). The disease-free interval between primary breast cancer and gastrointestinal involvement varies from synchronous presentation to up to 30 years[¹].