Which cellular structure is primarily evaluated in the diagnosis of cancer in histopathology?

The nucleus is primarily evaluated in the diagnosis of cancer in histopathology for several important reasons. In cancerous tissues, changes in the nucleus are often the most telling indicators of malignancy. These changes can include variations in size and shape (pleomorphism), an increased nuclear-to-cytoplasmic ratio, hyperchromasia (increased staining intensity due to dense packing of chromatin), and abnormal mitotic figures.

The nucleus contains the genetic material of the cell, and mutations or alterations in the DNA can lead to uncontrolled cell growth and cancer development. Pathologists assess these nuclear characteristics through microscopic examination and utilize scoring systems to quantify these features. Unlike other cellular structures, the nucleus provides the most direct insight into the genetic and molecular changes occurring in malignant cells, thus making it a key focal point in the diagnosis of cancer.

While mitochondria, cytoplasm, and cell membranes can also provide some information about cellular function and health, it is the nuclear abnormalities that are most reliably associated with neoplasia, therefore making the nucleus the primary structure evaluated in cancer diagnosis.