**Core Concept:** The penile carcinomas undergo invasion of surrounding tissues, including corpus spongiosum, which is a crucial determinant of their stage.

**Why the Correct Answer is Right:** In the context of carcinoma penis, stage classification takes into account the depth of invasion and involvement of surrounding structures. According to the TNM (Tumor, Node, Metastasis) staging system, when a tumor invades the corpus spongiosum (T2 stage), it is considered as T2. This staging classifies tumors as having invaded the corpora spongiosum but not the urethra.

**Why Each Wrong Option is Incorrect:**

A. Involving only the urethral mucosa: This corresponds to the T1 stage, as the tumor has invaded the urethral mucosa but not the corpus spongiosum.

B. Involving the urethral mucosa and corpus cavernosum: This would be T1 stage, as the tumor has invaded the urethral mucosa and corpus cavernosum but not corpus spongiosum.

C. Involving the corpus cavernosum without urethral invasion: This would be T2 stage, as the tumor has invaded the corpus cavernosum but not the urethra or corpus spongiosum.

D. Involving the urethral mucosa, corpus cavernosum, and corpus spongiosum: This would be T3 stage, as the tumor has invaded all three mentioned structures (urethral mucosa, corpus cavernosum, and corpus spongiosum).

**Clinical Pearl:** The staging of penile carcinomas is crucial for determining prognosis and treatment options. Knowing the stage helps in choosing the most appropriate treatment modality, such as surgery, radiation, or chemotherapy, and predicting the patient's prognosis.

**Correct Answer:** C. Involving the corpus cavernosum without urethral invasion. This corresponds to the T2 stage, where the tumor invades the corpus cavernosum but not the urethra or corpus spongiosum.