This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
Which of the following is true about pneumoconiosis? 
Select and explain. 
A. Pleural plaques of asbestosis is always symptomatic, B. Silicosis is never associated with tuberculosis, C. Asbestosis and smoking act synergistically to cause lung cancer, D. Anthracosis causes lung cancer
C: Asbestosis and smoking act synergistically to cause lung cancer
Answer: C: Asbestosis and smoking act synergistically to cause lung cancer 
Explanation: Lung cancer is the most common cancer associated with asbestos exposure.There is a significant inter-active effect of smoking and asbestos exposure that results in greater risk than what would be expected from the additive effect of each factor. Asbestos related pleural plaques,paicularly along the lower lung fields,the diaphragm, and the cardiac border,imply only exposure ,not pulmonary impairment & without additional manifestations.Since silica is cytotoxic to alveolar macrophages,patients with silicosis are at greater risk of acquiring tuberculosis. Reference:Harrison's medicine-18th edition,page no:2123-2125.