Adenocarcinomas are the most common primary lung cancer to develop within an area of peripheral scar. Scar tissue formation may be secondary to previous granulomatous disease (tuberculosis), infarction, or interstitial diseases of the lung associated with fibrosis (e.g., progressive systemic sclerosis). The pathogenesis of scar carcinoma is not completely understood. One theory is that scar tissue blocks lymphatic drainage, causing an increased concentration of anthracotic pigment-containing carcinogens. Persistent hyperplasia of tissue and the potential for a mutation leading to cancer are other mechanisms that may be similar to those of cancers that develop in fistulous tracts draining pus (e.g., chronic osteomyelitis).