Dark spots on the skin are very unlikely to be a sign you have lung cancer. Even if lung cancer spreads (metastasizes) to the skin, these skin metastases will usually appear as nodules, not hyperpigmentation.
Nodules are small, painless lumps. They may be firm or rubbery and red, pink, blue, or black.
Dark spots on your skin in the absence of other symptoms can have many sources, and most aren’t a cause for concern. Sun exposure and certain medications can result in hyperpigmentation.
If you have concerns about dark spots on your skin or you’re experiencing other symptoms along with hyperpigmentation, be sure to plan a visit with a doctor or dermatologist.