A week that I've had minor pain when I touch along the medial malleolus from inner left ankle; little swelling comes and goes. Worried its cancerous?

From what was stated. I would "guess" posterior tibial tendonopathy before cancer. Seek out a doctors visit to find your diagnosis and allay your fears.
Probably not. See doctor and get it checked out. Swelling on inner aspect of the ankle is usually from tendonitis particularly the posterior tibial tendon. Other causes are inflammation of the ankle joint or the start of a stress reaction. Get it sorted out so you dont have to worry about cancer there.