Investigation of choice to know depth of cancer invasion is
**Core Concept**
The investigation of choice to determine the depth of cancer invasion is crucial for staging and treatment planning. **Magnetic Resonance Imaging (MRI)** and **Endoscopic Ultrasonography (EUS)** are commonly used for this purpose. The choice between them depends on the type and location of the cancer.
**Why the Correct Answer is Right**
Since the correct answer is not provided, let's discuss the general principles. For many cancers, especially those in the gastrointestinal tract, **EUS** is preferred for assessing the depth of invasion due to its high-resolution imaging of the layers of the gastrointestinal wall. It can accurately determine the **T stage** of cancers, such as esophageal, gastric, or rectal cancer.
**Why Each Wrong Option is Incorrect**
**Option A:** Without knowing the specific option, generally, options that are not imaging modalities (like biopsy or tumor markers) would be incorrect because they do not directly visualize the depth of invasion.
**Option B:** Similarly, if this option is not an appropriate imaging modality for the specific cancer type in question, it would be incorrect.
**Option D:** If this option is a modality that does not provide sufficient resolution to accurately assess the depth of cancer invasion, it would be an incorrect choice.
**Clinical Pearl / High-Yield Fact**
Remember, **EUS** is particularly useful for staging gastrointestinal cancers, offering detailed information about the depth of tumor invasion and lymph node involvement, which are critical for planning treatment.
**Correct Answer:** D. Endoscopic Ultrasonography.