**Core Concept**
Gleason's score is a grading system used to evaluate the prognosis of patients with prostate cancer. It is based on the histological appearance of the tumor, with higher scores indicating a more aggressive form of the disease.

**Why the Correct Answer is Right**
Gleason's score is calculated by adding the grades of the two most prevalent tumor patterns in the prostate gland. The grades are based on the nuclear and cytoplasmic differentiation of the tumor cells, with Grade 1 indicating well-differentiated cells and Grade 5 indicating poorly differentiated cells. The score ranges from 2 to 10, with higher scores indicating a more aggressive tumor. This system helps clinicians to predict the behavior of the tumor and plan appropriate treatment.

**Why Each Wrong Option is Incorrect**
**Option A:** Gleason's score is not used for breast cancer.
* Incorrect because Gleason's score is a specific grading system for prostate cancer, not breast cancer.

**Option B:** Gleason's score is used to assess the response to chemotherapy.
* Incorrect because Gleason's score is a prognostic tool, not a measure of treatment response.

**Option C:** Gleason's score is based on the tumor's size and location.
* Incorrect because Gleason's score is based on the histological appearance of the tumor, not its size or location.

**Option D:** Gleason's score is used for all types of cancer.
* Incorrect because Gleason's score is a specific grading system for prostate cancer, not applicable to other types of cancer.

**Clinical Pearl / High-Yield Fact**
Gleason's score is an important prognostic factor for prostate cancer, and a score of 7 or higher is often associated with a higher risk of recurrence after treatment.

**Correct Answer: D. Gleason's score is used for prostate cancer.**