A 69-year-old male presents with fever, leukocytosis, and left lower quadrant pain. What is the likely diagnosis?

In this scenario, the combination of fever, leukocytosis (an elevated white blood cell count), and left lower quadrant pain strongly suggests diverticulitis. This condition arises when diverticula, which are small pouches that can form in the wall of the colon, become inflamed or infected.

The left lower quadrant is particularly relevant here, as diverticula are more commonly found in the sigmoid colon, which is located on the left side of the abdomen. The acute inflammation associated with diverticulitis often leads to systemic symptoms such as fever and leukocytosis, indicating a response to infection.

Other conditions listed, such as appendicitis, typically present with right lower quadrant pain, especially in older patients, and would likely not be the most plausible diagnosis here. Colorectal cancer can lead to some similar symptoms, but it usually presents differently and may not cause acute pain or a sudden increase in white blood cell count. Pancreatitis tends to cause upper abdominal pain radiating to the back, along with other specific symptoms, which do not align with the details provided in this case.

Therefore, given the specific presentation of symptoms, diverticulitis is the most likely diagnosis.