A Labor MP sworn into federal parliament just a fortnight ago has vowed to fight on after discovering her cancer had returned.

Peta Murphy, who won the Melbourne seat of Dunkley at the May 18 election, received the unexpected news last week that the cancer was back after five years in the clear.

“While this has come as a shock, my doctor advises me that my condition is treatable and that he expects me to do well with treatment, which I will start in the coming weeks,” Ms Murphy told The Age on Thursday.

“I have terrific support from family, friends and colleagues, and a strong fighting spirit.”

Liberal senator Arthur Sinodinos, who survived a battle with cancer, was among the first to wish her well.

“Good luck Peta, your spirit will pull you through. Don’t let the illness define you, there’s lots to do for your constituents,” he posted to Twitter.

Ms Murphy, 45, will deliver her first speech to parliament on July 24.