Can cancerous lumps grow then shrink then grow in size?

Usually they keep gr: Cancer is typically progresive in growth, regressions are extemely rare but it can happen once in a while. Mostly it just keeps getting bigger and then starts spreading into the body.

Not usually: However, some fast-growing cancers can grow so fast that there isn't enough blood flow to them and parts of the tumor die off due to lack of blood flow, resulting in temporary shrinkage in the overall tumor. Your question really needs to be addressed with a face-to-face doctor visit & exam, rather than over the internet, though. Good luck!