**Core Concept**
E-cadherin is a transmembrane glycoprotein that plays a crucial role in cell-cell adhesion, particularly in epithelial tissues. Its mutation or loss of expression can lead to a decrease in cell-to-cell adhesion, facilitating the process of metastasis.

**Why the Correct Answer is Right**
E-cadherin mutations are commonly associated with lobular breast carcinoma, a subtype of breast cancer characterized by its poor differentiation and high propensity for metastasis. The loss of E-cadherin function disrupts the normal adhesion between epithelial cells, allowing cancer cells to invade surrounding tissues and spread to distant sites. This is in contrast to ductal breast carcinomas, which tend to retain E-cadherin expression and are less likely to metastasize.

**Why Each Wrong Option is Incorrect**
**Option A:** E-cadherin mutations are not typically associated with ductal breast carcinomas, which are the most common type of breast cancer.
**Option B:** While mutations in the PI3K/AKT pathway can promote metastasis, they are not directly related to E-cadherin function.
**Option C:** The HER2/neu receptor is overexpressed in some breast cancers, but its overexpression is not directly linked to E-cadherin mutations.

**Clinical Pearl / High-Yield Fact**
In addition to E-cadherin, other adhesion molecules such as β-catenin and p120 catenin also play critical roles in maintaining cell-cell adhesion. Their dysregulation can contribute to the development and progression of various cancers.

**Correct Answer: C.**