Final answer:
The definitive diagnostic method for breast cancer is a biopsy, specifically a core needle biopsy, which provides a tissue sample for microscopic examination to confirm if cancer is present.
Step-by-step explanation:
Definitive Diagnostic Method of Breast Cancer
When diagnosing breast cancer, a biopsy is the definitive method for confirmation. Imaging techniques like mammography, ultrasound, and MRI can provide evidence of abnormalities in the breast tissue but cannot confirm the presence of cancer alone. Specifically, a core needle biopsy is a procedure where a needle is used to extract a tissue sample from the breast, which is then examined microscopically by a pathologist. This method can conclusively determine whether the tissue is malignant or benign, making it the correct answer to the student's question.
Other diagnostic techniques mentioned, such as mammography and ultrasound, are important screening tools used to detect any irregularities that may require further investigation through biopsy. A fine needle aspiration (FNA) is another type of biopsy that uses a thin needle to extract cells from a tumor, but a core needle biopsy generally provides a more conclusive diagnosis due to the larger amount of tissue that can be examined. While imaging techniques are essential in the detection process, the biopsy remains the gold standard for a definitive diagnosis of breast cancer.