**Core Concept**
Infiltrating lobular carcinoma (ILC) is a type of breast cancer that originates in the lobules, or milk-producing glands, of the breast. The histological features of ILC are distinct from those of ductal carcinoma, the most common type of breast cancer.

**Why the Correct Answer is Right**
ILC is characterized by the presence of signet-ring cells, which are large, mucin-filled cells that displace normal breast tissue. The signet-ring cells in ILC are typically positive for estrogen receptor (ER) and progesterone receptor (PR), and are often negative for HER2. The lobular carcinoma in situ (LCIS) component, if present, shows a loss of E-cadherin expression, which is a key feature of the disease. This loss of E-cadherin leads to the disruption of cell-cell adhesion and the characteristic infiltration of cancer cells into the surrounding stroma.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not describe a characteristic feature of ILC.
**Option B:** This option is incorrect because it does not accurately describe the histology of ILC.
**Option C:** This option is incorrect because it does not mention the key histological feature of signet-ring cells in ILC.

**Clinical Pearl / High-Yield Fact**
ILC often presents as a diffuse, ill-defined mass on imaging, and may be associated with a higher risk of bilaterality and recurrence compared to ductal carcinoma. The presence of signet-ring cells in ILC is a key diagnostic feature, and the loss of E-cadherin expression is a useful marker for this type of cancer.

**Correct Answer: C. Signet-ring cells are a characteristic feature of infiltrating lobular carcinoma.**