Porth's Essentials of Pathophysiology, 4e

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Cell and Tissue Function

U N I T 1

Common Paraneoplastic Syndromes

 TABLE 7-3

Type of Syndrome

AssociatedTumorType

Proposed Mechanism

Endocrinologic Syndrome of inappropriate ADH

Small cell lung cancer, others Small cell lung cancer, bronchial carcinoid cancers Squamous cell cancers of the lung, head, neck, ovary

Production and release of ADH by tumor Production and release of ACTH by tumor

Cushing syndrome

Hypercalcemia

Production and release of polypeptide factor with close relationship to PTH

Hematologic Venous thrombosis

Pancreatic, lung, other cancers

Production of procoagulation factors

Nonbacterial thrombolytic endocarditis Neurologic Eaton-Lambert syndrome

Advanced cancers

Small cell lung cancer

Autoimmune production of antibodies to motor end-plate structures

Myasthenia gravis

Thymoma

Dermatologic Acanthosis nigricans

Gastric carcinoma

Possibly caused by production of growth factors (epidermal) by tumor cells

ACTH, adrenocorticotropic hormone; ADH, antidiuretic hormone; PTH, parathyroid hormone.

hematologic complications. 47 For example, a variety of cancers may produce procoagulation factors that contribute to an increased risk for venous thrombosis and nonbacterial thrombotic endocarditis. Sometimes, unexplained thrombotic events are the first indication of an undiagnosed malignancy. The precise relation- ship between coagulation disorders and cancer is still unknown.Severalmalignancies,suchasmucin-producing adenocarcinomas, release thromboplastin and other substances that activate the clotting system. The symptomatic paraneoplastic neurologic dis- orders are relatively rare with the exception of the Lambert-Eaton myasthenic syndrome, which affects about 3% of persons with small cell lung cancer, and myasthenia gravis, which affects about 15% of people with thymoma. 48,49 The Lambert-Eaton syndrome , or reverse myasthenia gravis, is seen almost exclusively in small cell lung cancer. It produces muscle weakness in the limbs rather than the initial mouth and eye muscle weakness seen in myasthenia gravis. The origin of para- neoplastic neurologic disorders is thought to be immune mediated. The altered immune response is initiated by the production of onconeural antigens (e.g., antigens normally expressed in the nervous system) by the can- cer cells. The immune system, in turn, recognizes the onconeural antigens as foreign and mounts an immune response. In many cases, the immune attack controls the growth of the cancer. The paraneoplastic syndromes may be the earliest indication that a person has cancer, and should be regarded as such. They may also represent significant clinical problems, may be potentially lethal in persons with cancer, and may mimic metastatic disease and con- found treatment. Diagnostic methods focus on both identifying the cause of the disorder and locating the malignancy responsible. Techniques for precise identifi- cation of minute amounts of polypeptides may allow for

early diagnosis of curable malignancies in asymptomatic individuals. The treatment of paraneoplastic syndromes involves concurrent treatment of the underlying cancer and suppression of the mediator causing the syndrome.

SUMMARY CONCEPTS

■■ There probably is no single body function left unaffected by the presence of cancer. Because tumor cells replace normally functioning parenchymal tissue, the initial manifestations of cancer usually reflect the primary site of involvement. ■■ Cancer compresses blood vessels, obstructs lymph flow, disrupts tissue integrity, invades serous cavities, and compresses visceral organs. It may result in development of effusions (i.e., fluid) in the pleural, pericardial, or peritoneal spaces. ■■ Systemic manifestations of cancer include anorexia and cachexia; fatigue and sleep disorders; and anemia. ■■ Cancer may also produce paraneoplastic syndromes that arise from the ability of neoplasms to elaborate hormones and other chemical mediators to produce endocrine, hematopoietic, neurologic, and dermatologic syndromes. Many of these manifestations are compounded by the side effects of methods used to treat the disease.