[Under the mask of Crohn's disease. A clinical case report]

Invasive lobular breast carcinoma is characterized by infiltrative growth and a tendency toward atypical metastasis, including to the gastrointestinal tract, where metastases are often diffusely infiltrative, complicating their visualization and potentially leading to diagnostic errors. This paper presents a clinical case of a 55-year-old female patient with long-standing (approximately 20 years) abdominal pain syndrome. Based on imaging studies and elevated fecal calprotectin levels, this pain syndrome was interpreted as Crohn's disease, despite the lack of response to standard therapy. One year after confirmation of invasive lobular breast cancer (luminal A subtype, T1N1M0), the patient continued to experience abdominal symptoms until the development of dynamic intestinal obstruction, which required surgical intervention. Histological and immunohistochemical examination of the resected intestinal segment confirmed metastatic involvement of the small and large intestines. This case demonstrates a rare variant of lobular breast cancer metastasis to the intestine, which had been masquerading as Crohn's disease for a long time. It highlights the need for oncological vigilance in patients with abdominal symptoms and a history of cancer, as well as the crucial role of immunohistochemistry in verifying the diagnosis.