Appendiceal cancer is one of the rarest tumors. In most patients, this disease is diagnosed during appendectomy or after autopsy. The authors report a patient with appendiceal cancer identified during the treatment of appendicular infiltrate and analyze literature devoted to this issue. Clinical case confirms that appendiceal cancer is difficult for differential diagnosis due to peculiarities and variability of its course. This aspect prevents timely treatment of disease. Timely and accurate diagnosis requires not only clinical experience, but also introduction of new technologies and clinical tests that could reduce the risk of damage and increase the accuracy of diagnostic data.