**Core Concept**
Tumor cells in hypoxic environments exhibit increased resistance to chemotherapy and radiation due to their slower rate of cell division and activation of DNA repair mechanisms. Chemotherapeutic agents that selectively target these cells can improve treatment outcomes by killing the most resistant tumor cells.

**Why the Correct Answer is Right**
The chemotherapeutic drug that selectively targets hypoxic tumor cells is **Tirapazamine**. Tirapazamine is a hypoxia-selective cytotoxin that is activated under low oxygen conditions, leading to DNA damage and cell death in hypoxic tumor cells. This is because the drug is reduced to its active form by low levels of oxygen, which are characteristic of hypoxic tumor cells. Tirapazamine has been shown to enhance the effectiveness of conventional chemotherapy and radiation therapy in clinical trials.

**Why Each Wrong Option is Incorrect**
* **Option A:** Other chemotherapeutic agents, such as etoposide and irinotecan, do not have selective action on hypoxic tumor cells.
* **Option B:** Cisplatin is a platinum-based chemotherapeutic agent that is activated under normal oxygen conditions, making it less selective for hypoxic tumor cells.
* **Option C:** Doxorubicin is an anthracycline antibiotic that is not specifically targeted towards hypoxic tumor cells.

**Clinical Pearl / High-Yield Fact**
Tirapazamine is an example of a hypoxia-selective cytotoxin that can be used in combination with conventional chemotherapeutic agents to improve treatment outcomes in patients with solid tumors.

**Correct Answer:** C. Tirapazamine.