**Core Concept**
Mammography is a crucial diagnostic tool for breast cancer detection, and various features can indicate malignancy. The features of a malignant tumor on mammogram include architectural distortion, microcalcifications, and irregular masses. Macrocalcifications, on the other hand, are typically associated with benign conditions.

**Why the Correct Answer is Right**
Macrocalcifications are usually seen in benign conditions such as fibroadenomas or fibrocystic changes. They appear as large, coarse calcifications that are often diffuse and irregular. In contrast, microcalcifications are small, punctate calcifications that are highly suggestive of malignancy, particularly if they are clustered or have a linear or segmental distribution. Irregular masses and spiculation are also characteristic of malignant tumors, which can cause architectural distortion and irregular margins.

**Why Each Wrong Option is Incorrect**
**Option A:** Spiculation is a feature of malignant tumors, which can cause architectural distortion and irregular margins.
**Option B:** Microcalcification is a highly suggestive feature of malignancy, particularly if they are clustered or have a linear or segmental distribution.
**Option D:** Irregular mass is a characteristic of malignant tumors, which can be round, oval, or irregular in shape.

**Clinical Pearl / High-Yield Fact**
Remember the "BI-RADS" system for mammography, which categorizes breast lesions into categories based on their likelihood of malignancy. A BI-RADS 5 or 6 indicates a high suspicion of malignancy, while a BI-RADS 0 indicates additional imaging or biopsy is needed.

**✓ Correct Answer: C. Macrocalcification. Macrocalcifications are typically associated with benign conditions.**