**Core Concept**
Muscle-invasive bladder cancer is a type of non-metastatic bladder cancer where the tumor has grown into the muscle layer of the bladder wall, increasing the risk of metastasis and necessitating more aggressive treatment.

**Why the Correct Answer is Right**
The treatment of choice for muscle-invasive bladder cancer is radical cystectomy, which involves the surgical removal of the bladder, surrounding tissues, and lymph nodes. This approach is preferred over other treatments like chemotherapy, radiation, or partial cystectomy due to its high success rate in eradicating the cancer. In patients with muscle-invasive bladder cancer, the goal is to remove the bladder and all affected tissues to prevent further disease progression.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect as it does not specify a treatment for muscle-invasive bladder cancer. Chemotherapy or radiation therapy may be used as neoadjuvant or adjuvant therapy, but they are not the primary treatment for muscle-invasive disease.
**Option B:** This option is incorrect as partial cystectomy is typically reserved for small, superficial tumors that are confined to the bladder mucosa and have a low risk of recurrence.
**Option C:** This option is incorrect as immunotherapy is a relatively new treatment modality for bladder cancer, primarily used in non-muscle invasive disease or as part of a clinical trial.

**Clinical Pearl / High-Yield Fact**
Radical cystectomy is the gold standard treatment for muscle-invasive bladder cancer, with a 5-year survival rate of approximately 50-60% for patients undergoing this procedure.

**Correct Answer: C. Radical cystectomy.**