Histopathology: old principles and new methods.

Histopathology remains the benchmark and the only reliable means for diagnosing breast cancer in either invasive or preinvasive stages and for classifying morphologically distinct special types of breast cancer that exhibit different prognoses. Careful epidemiological research performed in tandem with histopathology had demonstrated that certain preinvasive lesions progress to invasive cancer at high frequency, and the detection of these lesions seems certain to increase with increased mammographic screening. Comedo and non-comedo DCIS represent examples of distinct preinvasive lesions in which differing histopathology reflects altered biological behaviour. Certain morphological varieties of invasive cancer are also associated with different biological outcomes, notably the special histological types such as tubular, lobular and medullary. Distinguishing these heterogeneous forms of breast cancer is crucial for diagnosis, prognostic prediction and the acquisition of research material for clinically relevant molecular epidemiological studies.