Beyond Boundaries: Breast Cancer Metastasizing to Colon-An Insight into a Rare yet Significant Clinical Scenario: A Case Series.

Background: Colorectal metastasis from primary breast cancer is rare and presents a challenge for diagnosis and treatment. Aim: To report two cases of colorectal metastasis from a primary invasive lobular breast carcinoma (ILBC) with different presentations while discussing the mode of diagnosis, immunohistochemistry (IHC), course of treatment, and response. Case descriptions: Case 1: A 47-year-old female, with a known case of bilateral invasive lobular breast cancer, was diagnosed in 2015 and staged as p Tx N3 M0. She underwent a bilateral nipple-sparing mastectomy and presented 8 years later with complaints of left-sided abdominal pain and altered bowel habits for 2 months. She underwent a colonoscopy, and an erythematous area was noted in the ascending colon, and narrowings were seen in the transverse and rectosigmoid junction. Histopathological findings were consistent with metastatic ILBC with the same IHC pattern. Case 2: A 52-year-old woman presented in September 2019 with a 1-month history of constipation, generalized colicky abdominal pain, 7 kg weight loss, nausea, and anorexia. She underwent a colonoscopy, which revealed a malignant-appearing apple-core lesion at the proximal rectum with severe stenosis that could not be bypassed. A PET-CT showed suspicious breast lesions, and after further investigations and biopsies, she was diagnosed with primary invasive lobular carcinoma (ILC) of the breast with rectal metastasis. Clinical significance: With the increasing incidence of both colorectal and breast cancer and the rarity of breast cancer metastasis to the gastrointestinal tract (GIT), this case series aims to highlight the growing incidence of lobular breast cancer metastasis to the colon and to shed light on the importance of further research in this area in terms of early detection and treatment to improve the prognosis of such patients. Conclusion: This case series highlights the clinical presentations, diagnosis, histopathology, challenges, and trials of treatment in our patients. These findings show the importance of considering gastrointestinal (GI) involvement in breast cancer patients and the need for multidisciplinary approaches to achieve better outcomes. However, this is an area of need for more research and awareness to improve the understanding and management of GI metastases from breast cancer. How to cite this article: Saeed MF, Rahma SH, Alrabeea MS,