**Core Concept**
Mammography is a crucial tool for breast cancer screening, and identifying features of malignant tumors is essential for accurate diagnosis. The American College of Radiology (ACR) and the Society of Breast Imaging (SBI) have established guidelines for mammographic features of breast lesions.

**Why the Correct Answer is Right**
Malignant breast tumors often exhibit irregular margins, microcalcifications, and spiculations, which are indicative of infiltration into surrounding tissues. These features are caused by the aggressive cellular growth and invasion of malignant cells into the surrounding breast tissue. The presence of these features on a mammogram raises suspicion for malignancy and warrants further investigation. In contrast, benign lesions typically have smooth, well-defined margins and may exhibit calcifications that are round, oval, or linear.

**Why Each Wrong Option is Incorrect**
* **Option A:** Irregular margins are a feature of malignant tumors, so this option is incorrect.
* **Option B:** Microcalcifications are often associated with malignant tumors, particularly ductal carcinoma in situ (DCIS), so this option is incorrect.
* **Option C:** Spiculations are another feature of malignant tumors, indicating infiltration into surrounding tissues, so this option is incorrect.

**Clinical Pearl / High-Yield Fact**
When interpreting mammograms, remember the "ABCs" of malignancy: Asymmetry, Border irregularity, and Calcifications. These features can help differentiate malignant from benign lesions.

**Correct Answer: A. Irregular margins are a feature of malignant tumors, so this option is incorrect.**