Both reactivation tuberculosis (TB) and primary squa­mous-cell carcinoma of the lung are associated with cavitation. Other pulmonary diseases associated with cavitation include systemic fungal infections, Klebsiella pneumonias, and silicosis. In silicosis, the large fibrotic nodules undergo central necrosis from ischemia. Fur­thermore, silicosis predisposes patients to the develop­ment of TB within the fibrotic nodules, thus produc­ing cavitation. Ectopic secretion of a parathormone-like peptide producing hypercalcemia is seen only in squamous cell carcinoma. Scar carcinomas are a possible sequela of old scar tissue in TB. Adenocarcinomas are more frequently associated with scar carcinomas than squa­mous carcinoma. The most common extrapulmonary site for TB is the kidneys, and the adrenal gland is the most common site for metastatic squamous cancer. Silicosis predisposes patients to TB, but not to primary lung cancer.