Is It Safe To Take Methotrexate To Treat Plaque Psoriasis?

My mom suffers from severe plaque psoriasis. She was taking enbrel until it stopped working for her. Now she is taking stelara but it is no longer effective as it once was when first taking it. This drug is known to increase chances of skin cancer which has her concerned as she has already had three precancerous spots removed from her leg within the last 6 months. Our local docs tell her that there's nothing else she can take, as she's on the strongest psoriasis medication. Is this true? I researched and found that methotrexate is used as an anti-cancer drug as well as a treatment for psoriasis. Should her docs be considering this option? Seems this would cure both of her problems that have sent her into depression, precancerous and psoriasis.