Cancer: A proliferation of cells whose unique trait - loss of normal controls - results in unregulated growth, lack of differentiation, local tissue invasion, and metastasis.
Cancer (malignancy) can develop in any tissue of any organ at any age. Most cancers are potentially curable if detected at an early stage. By performing self-examinations, patients can help recognize early signs of some possible malignancies. Diagnostic testing and therapy are essential for optimal results. When cure or reasonable palliation is likely, physicians must discuss all therapeutic options.
Patients with cancer that is unlikely to be cured need to be informed about what treatment is likely to accomplish and the side effects it may produce. Intensive care may be needed for treatment-related complications. Psychologic support from the physician and the health care team (which may include a psychiatrist and a social worker) helps patients through therapy (see Complications, below).
Physicians must be truthful, yet convey a sense of optimism. Some patients may need to be advised against health care practitioners who falsely promise cure. The patient should feel that members of the health care team are concerned and available to answer questions. The physician should initiate frank discussions about end-of-life care and advance medical directives at an appropriate time.
Cellular Kinetics
Generation time is the time it takes for cells to enter the cell cycle (see Fig. 142-1) and give rise to two daughter cells. Malignant cells usually have a shorter cycle than nonmalignant cells. Most nonmalignant cells have a larger percentage of cells in G0 (resting phase), so that there is a smaller proliferation fraction. Initial exponential tumor growth is followed by a plateau phase when cell death equals the rate of formation of daughter cells. Compared with large tumors, small tumors have a greater percentage of cells in cycle and thus greater proliferation.
Cellular kinetics are important in the design of antineoplastic drug regimens. Many antineoplastic drugs are effective only if cells are in cell cycle, and some drugs work only during a specific phase of the cycle. Cellular kinetics may influence the dosage schedules and timing of treatment.
Tumor Growth and Metastasis
As a tumor grows, nutrients are provided by direct diffusion from the circulation. Local tissue invasion can result in pressure on normal tissues, which can lead to inflammation, or the tumor may produce substances (eg, collagenase) that lead to enzymatic destruction of tissues. Subsequently, synthesis of tumor angiogenesis factor causes formation of an independent vascular supply to the tumor. Almost from inception, a tumor may shed cells into the circulation.
