A thymoma is a tumor that starts in the thymus, a small gland behind the breastbone. It grows slowly, so symptoms can be vague until it presses on nearby structures or triggers immune problems. Chest pressure is the first clue. You feel a tight, heavy weight behind the breastbone, especially when lying flat. Cough that won’t quit shows up next. It’s dry and hacking, caused by the tumor pressing on the windpipe. Shortness of breath creeps in. You puff on stairs or can’t finish a sentence without pausing. Fatigue is common. Muscles feel heavy, and you need naps even after... Learn more