Cancer is a progressive disease that usually begins with increased frequency of cell division (Figure 13.2). Under the microscope, this may be detectable as increased cellular and nuclear size, and an increased proportion of cells undergoing mitosis. As the disease progresses, cells typically lose their normal shape and tissue organization. Tissues with increased cell division and abnormal tissue organization exhibit dysplasia. Eventually a tumor develops, which can grow rapidly and expand into adjacent tissues.
Figure 13.2: Progressive increases in cell division and abnormal cell morphology associated with cancer. (Wikipedia-NIH-PD)
As cellular damage accumulates and additional control mechanisms are lost, some cells may break free of the primary tumor, pass into the blood or lymph system, and be transported to another organ, where they develop into new tumors (Figure 13.3). The early detection of tumors is important so that they can be treated or removed before the onset of metastasis, but note that not all tumors will lead to cancer. Tumors that do not metastasize are classified as benign, and are not usually considered life threatening. In contrast, malignant tumors become invasive, and ultimately result in cancer.
Figure 13.3: Secondary tumors (white) develop in the liver from cells of a metastatic pancreatic cancer. (Wikipedia-J. Hayman-PD)
Dr. Todd Nickle and Isabelle Barrette-Ng (Mount Royal University) The content on this page is licensed under CC SA 3.0 licensing guidelines.