Costochondritis: This is an inflammation of the cartilage that connects the ribs to the sternum. It is a common cause of sharp pain on the sternum and can cause pain with breathing, especially when taking deep breaths. The pain is usually sharp and stabbing, and can be reproduced by pressing on the affected area.

Musculoskeletal strain: Strain or pull of the muscles or ligaments in the chest wall can cause sharp pain on the sternum and pain with breathing.
Rib fracture: A fracture of one or more ribs can cause sharp pain on the sternum and pain with breathing, especially if the fracture is near the sternum.
Precordial catch syndrome: This is a benign condition that causes sharp pain on the sternum, often triggered by deep breathing or movement.

Myocardial infarction (heart attack): Although less common, myocardial infarction can cause sharp pain on the sternum and pain with breathing. It is essential to consider this diagnosis, especially in patients with risk factors for heart disease.
Pulmonary embolism: A blood clot in the lungs can cause sharp pain on the sternum and pain with breathing, especially if the clot is large or located near the main pulmonary arteries.
Aortic dissection: A tear in the aorta can cause sharp pain on the sternum and pain with breathing, especially if the tear is near the aortic root.

Tietze's syndrome: This is a rare condition that causes inflammation of the cartilage and surrounding tissues in the chest wall, leading to sharp pain on the sternum and pain with breathing.
Sternal fracture: A fracture of the sternum itself is rare but can cause sharp pain on the sternum and pain with breathing.
Mediastinitis: Inflammation of the tissues in the mediastinum (the area between the lungs) can cause sharp pain on the sternum and pain with breathing, although this is a rare condition.