ABSTRACT
Lactic acidosis associated with solid neoplasms is a rare complication; its occurrence is poorly described, and it is associated with a poor prognosis. We present the case of an 84-year-old woman who was admitted to the internal medicine department with a diagnosis of urinary tract infection accompanied by a blood gas analysis showing lactic acidosis. During her admission, an abdominal mass was evidenced and finally diagnosed as undifferentiated carcinoma. We wanted to emphasize the importance of correlating clinical and laboratory data at the time of making a diagnostic approach and also highlight other possible explanations of lactic acidosis that should be considered in addition to hypoperfusion due to sepsis, especially in the elderly who are at increased risk of malignancy.