Pancoast tumors are a rare type of lung cancer that develops in the apex (top part) of one of your lungs.

Horner syndrome is a rare neurological condition affecting your nervous system. In this case, the affected nerve pathways involve your face and eye, causing symptoms like a drooping eyelid.

Although both conditions are rare, Horner syndrome is a common feature of Pancoast tumors.

When cancers develop deep inside your lungs, they first spread elsewhere in your lungs before moving to nearby lymph nodes and other organs.

However, your lung’s apex is near the nerve pathways connecting your brain stem to your face and eyes. So, when a Pancoast tumor spreads, it can more easily invade nerves along this pathway, leading to classic symptoms of Horner syndrome, such as:

These symptoms occur on the same side as your affected lung.

Treating the underlying Pancoast tumor may help restore regular nerve function. The standard treatment for Pancaost tumors is chemotherapy and radiation therapy, followed by surgery.

People with Horner syndrome can undergo surgery unless the cancer spreads further (specifically, above the T1 nerve root).

But by the time Pancoast tumors cause Horner syndrome, some degree of metastasis exists, meaning that the tumor may be more challenging to treat successfully.

The key to a successful treatment is early detection. Pancoast tumors don’t usually present with typical lung cancer symptoms like coughing or shortness of breath. Most people (up to 96%) experience shoulder pain as the initial symptom.

Talking with a doctor can help prevent complications like Horner syndrome and improve your chances of a successful treatment if you’re at risk of lung cancer and experience symptoms of a Pancoast tumor.