Mariena Browning, 28, from Pocatello, Idaho, was diagnosed with stage 3 melanoma after finding a lump in her groin at 22 years old—a relatively unusual spot for this dangerous type of skin cancer.

There are a number of less common symptoms such as itching and changes to bowel habits. If the cancer has spread to the lymph nodes in the groin, they may be swollen. But some people do not have any ...