**Core Concept**
Gleason's staging is a system used to grade prostate cancer based on the microscopic appearance of the tumor. It takes into account the pattern and grade of the tumor's glandular differentiation, with higher scores indicating more aggressive cancer.

**Why the Correct Answer is Right**
The Gleason score is calculated by adding the grades of the two most prevalent patterns of tumor growth in the biopsy sample. This grading system helps predict the cancer's behavior, treatment outcomes, and prognosis. The grades range from 1 to 5, with 1 being well-differentiated and 5 being poorly differentiated. The score is used to categorize prostate cancer into five stages: Stage 1 (Gleason score 2-4), Stage 2 (Gleason score 5-6), Stage 3 (Gleason score 7), Stage 4 (Gleason score 8-10), and Stage 5 (Gleason score 10). The Gleason score is a key factor in determining the appropriate treatment plan for prostate cancer.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Gleason's staging is not used for other types of cancer, such as breast or colon cancer. While other grading systems are used for these cancers, Gleason's staging is specific to prostate cancer.

**Option B:** This option is incorrect because Gleason's staging is not a prognostic index, although it is used to predict cancer behavior and treatment outcomes. While prognosis is an important consideration in cancer treatment, Gleason's staging is not a direct measure of prognosis.

**Option C:** This option is incorrect because Gleason's staging is not a surgical staging system. While surgical staging may be used in some cases, Gleason's staging is based on the microscopic examination of biopsy samples.

**Clinical Pearl / High-Yield Fact**
The Gleason score is an important prognostic factor in prostate cancer, and a higher score is associated with a worse prognosis. It's essential to remember that the Gleason score is just one factor in determining treatment plans, and other factors such as age, overall health, and cancer stage are also considered.

**Correct Answer:** C.