**Core Concept**
Male breast cancer is a rare but distinct entity with its own histopathological characteristics. The majority of male breast cancers are hormone receptor-positive, which means they are driven by the presence of estrogen and/or progesterone receptors.

**Why the Correct Answer is Right**
The most common type of male breast cancer is invasive ductal carcinoma, accounting for approximately 70-80% of cases. This type of cancer arises from the ductal epithelium of the breast tissue and invades into the surrounding stroma. The presence of estrogen receptors (ER) and progesterone receptors (PR) in these tumors suggests that they are hormone-dependent, and their growth can be influenced by hormonal therapies.

**Why Each Wrong Option is Incorrect**
**Option A:** Lobular carcinoma in situ (LCIS) is a condition characterized by the proliferation of abnormal cells within the lobules of the breast tissue. While LCIS is often associated with an increased risk of developing breast cancer, it is not a type of invasive cancer.

**Option B:** Medullary carcinoma is a rare subtype of breast cancer that is characterized by a distinct histological appearance, with a prominent lymphocytic infiltrate. However, it is more common in women than men.

**Option C:** Tubular carcinoma is a rare subtype of invasive breast cancer that is characterized by a tubular or cribriform growth pattern. While it is a distinct entity with a good prognosis, it is not the most common type of male breast cancer.

**Clinical Pearl / High-Yield Fact**
The risk of male breast cancer is increased in men with a family history of breast cancer, particularly in those with a BRCA2 mutation.

**Correct Answer:** C. Invasive ductal carcinoma.