**Core Concept**
The question is asking about the prognosis or life expectancy of patients with different types of cancer. Cancer is a group of diseases characterized by the uncontrolled growth and spread of abnormal cells. The life expectancy of patients with cancer varies greatly depending on the type, stage, and aggressiveness of the disease.

**Why the Correct Answer is Right**
To determine which cancer has the least life expectancy, we need to consider the general prognosis of each type. **Pancreatic cancer** is known for its poor prognosis due to its late presentation, aggressive nature, and resistance to treatment. The 5-year survival rate for pancreatic cancer is around 9%, which is one of the lowest among all cancers. This is because pancreatic cancer often spreads to other parts of the body before it is diagnosed, making it difficult to treat.

**Why Each Wrong Option is Incorrect**
* **Option A:** Lung cancer, while aggressive, has a slightly better prognosis than pancreatic cancer, especially if caught early.
* **Option B:** Colorectal cancer, if detected early, has a high cure rate and a relatively good prognosis.
* **Option C:** Stomach cancer, while rare in Western countries, has a relatively better prognosis than pancreatic cancer, especially if treated early.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the prognosis of cancer patients depends on various factors, including the type of cancer, stage at diagnosis, and overall health of the patient. Early detection and treatment are crucial in improving life expectancy.

**Correct Answer:** C. Stomach cancer has a relatively better prognosis than pancreatic cancer.