Porth's Essentials of Pathophysiology, 4e

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Respiratory Tract Infections, Neoplasms, and Childhood Disorders

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carcinoma tends to originate in the central bronchi as an intraluminal growth and is thus more amenable to early detection through cytologic examination of the sputum than other forms of lung cancer. 13 It tends to spread cen- trally into major bronchi and adjacent intrapulmonary lymph nodes (Fig 22-9). Central cavitation of the tumor is frequent. Currently, adenocarcinoma is the most common sub- type of lung cancer in North America. 13,14 Its association with cigarette smoking is weaker than for squamous cell carcinoma. It is the most common type of lung cancer in women and nonsmokers. Adenocarcinoma is a malig- nant epithelial cell tumor with glandular differentiation or mucin production by the tumor cells. These tumors tend to be located more peripherally than squamous cell sarcomas and are often associated with pleural fibrosis and scarring (Fig. 22-10). In general, adenocarcinomas have a poorer stage-for-stage prognosis than squamous cell carcinomas. Large cell carcinomas have large, polygonal cells. They constitute a group of neoplasms that are highly anaplastic and difficult to categorize as squamous cell carcinoma or adenocarcinoma. They tend to occur in the periphery of the lung, invading subsegmental bron- chi and larger airways. They have a poor prognosis because of their tendency to spread to distant sites early in their course. 13,14 Small Cell Lung Cancer Small cell lung cancer is characterized by a distinctive cell type—small round to oval cells that are approxi- mately the size of a lymphocyte. 13,14,49,50 The cells grow in clusters that exhibit neither glandular nor squamous organization. The tumors are thought to arise from the neuroendocrine cells of the bronchial epithelium, and FIGURE 22-9. Squamous cell carcinoma of the lung in which the tumor grows within the lumen of a bronchus and invades the adjacent intrapulmonary lymph node. (From Beasley MB, TravisWD, Rubin E.The respiratory system. In: Rubin R, Strayer DS, eds. Rubin’s Pathology: Clinicopathologic Foundations of Medicine. 6th ed. Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams &Wilkins; 2012:595.)

some of the tumor cells may be able to secrete hormon- ally active products. This cell type is associated with several types of paraneoplastic syndrome (signs and symptoms caused by secretions of or immune response to tumor cells), including the syndrome of inappropriate antidiuretic hormone secretion (SIADH; see Chapter 8). This type of cancer has the strongest association with cigarette smoking and is rarely observed in someone who has not smoked. Small cell lung cancer is highly malignant, tends to infiltrate widely, disseminate early, and is rarely resect- able. About 70% of the cancers have detectable metasta- ses at the time of diagnosis; the rest are assumed to have micrometastases. Brain metastases are particularly com- mon with SCLC and may provide the first evidence of the tumor. Response rates for treatment with chemother- apy (cisplatin and etoposide) are excellent, with 50% to 60% complete response in persons with limited disease and 15% to 20% complete response in those with exten- sive disease. 47 However, remissions tend to be short-lived with a mean duration of 6 to 8 months. Once the disease has recurred, the mean survival length is 3 to 4 months. Overall the 2-year survival is 20% to 40% in limited- stage disease and less than 5% in extensive disease. Clinical Features Lung cancers are aggressive, locally invasive, and widely metastasizing tumors. Squamous cell and adenocarcino- mas usually begin as small mucosal lesions that may fol- low one of several patterns of growth. They may form intraluminal masses that invade the bronchial mucosa and infiltrate the peribronchial connective tissue, or they may form large, bulky masses that extend into the adjacent lung tissue. Some large tumors undergo FIGURE 22-10. Adenocarcinoma of the lung. A peripheral tumor is located in the upper right lobe of the lung. (From Beasley MB,TravisWD, Rubin E.The respiratory system. In: Rubin R, Strayer DS, eds. Rubin’s Pathology: Clinicopathologic Foundations of Medicine. 6th ed. Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams &Wilkins; 2012:595.)