9 signs of sneaky lung cancer symptoms the most common symptom of lung cancer is that “people don’t actually have any symptoms!” explains Nathan Pennell, M.D., Ph.D., a medical oncologist at Cleveland Clinic’s Taussig Cancer Center in Ohio. Given that, he says your best bet is to stay alert to “anything that just doesn’t go away when it should.” If any of the following symptoms linger longer than a month or so without an obvious explanation, alert the doctor, he says. Most of the time it won’t be cancer. “It will be normal stuff!” he says. But awareness pays: Lung cancer is sometimes curable when caught early. Here’s what to watch for.