A 62-year-old man is evaluated for a 4-month history of persistent cough and hemoptysis. He smoked one pack of cigarettes daily for 40 years and quit 2 years ago. For 25 years he worked in a shipyard removing and replacing pipe insulation. Chest CT shows a 3.2 cm spiculated mass in the right upper lobe. CT-guided biopsy reveals squamous cell carcinoma.
Which of the following best characterizes how this patient's tobacco use and occupational asbestos exposure interact to produce his bronchogenic carcinoma risk?