**Core Concept**
Cystosarcoma phyllodes is a rare type of breast tumor that belongs to the family of fibroepithelial tumors. It is characterized by its rapid growth and potential for local recurrence, but it is generally not malignant.

**Why the Correct Answer is Right**
The treatment of cystosarcoma phyllodes involves a multidisciplinary approach, including surgical excision with clear margins. The goal is to remove the tumor completely while preserving as much breast tissue as possible. In some cases, wide local excision may be necessary, especially if the tumor is large or has a high risk of recurrence. The type of surgery performed depends on the size, location, and histological characteristics of the tumor.

**Why Each Wrong Option is Incorrect**
**Option A:** Mastectomy is generally not the primary treatment for cystosarcoma phyllodes, as it is a localized tumor that can often be managed with less extensive surgery.
**Option B:** Radiation therapy is not typically used as a primary treatment for cystosarcoma phyllodes, although it may be considered in cases of recurrent disease or if the tumor has a high risk of local recurrence.
**Option C:** Chemotherapy is not usually indicated for the treatment of cystosarcoma phyllodes, as this tumor type is generally not malignant and has a low risk of distant metastasis.

**Clinical Pearl / High-Yield Fact**
It's essential to note that cystosarcoma phyllodes has a distinct histological appearance, characterized by a mixture of epithelial and stromal components, which can help differentiate it from other types of breast tumors.

**Correct Answer:** C. Wide local excision with clear margins is the preferred treatment for cystosarcoma phyllodes.