Objective: Rare disease Background: Sarcomatoid carcinomas have long been reported as uncommon, highly aggressive, and fatal neoplasms. They have been found to originate from different organs, including, but not limited to, the female genital tract, head and neck, and, less commonly, the gastrointestinal tract. Consequently, the clinical presentation is highly variable, misleading practitioners, impeding early correct diagnosis, and delaying management. In fact, most patients present with symptoms related to distant metastases. Due to its rarity, no guidelines for treatment have been set, leaving practitioners powerless facing this devastating tumor with an overall survival time not exceeding a few months. Case Report: In this article, we report a case of colonic sarcomatoid carcinoma with an extremely fast growth. The patient presented only after 1 week of constipation and investigations revealed a large sigmoidal tumor with a very aggressive, invasive, and fatal progression. Histologic evaluation and immunohistochemistry established the diagnosis. Unfortunately, despite adequate management, the patient died a few weeks after diagnosis. Conclusions: Although sarcomatoid carcinomas have been studied, colonic cases remain limited, with highly variable clinical presentations, showing the huge need for further research to unravel their pathophysiology, widen our comprehension, and establish an effective treatment plan for these patients.