Two months ago the 39-year-old western Sydney MP announced she was taking leave to undergo treatment to remove a large tumour on her kidney.

"My tumour ended up being so aggressive that it was double the size of what was predicted," Ms Car said in a statement on Monday.

"While I will need to undergo regular surveillance testing, the surgery to remove the tumour was successful."

She thanked the medical professionals who cared for her noting without their efforts, "things could have turned out very differently for me".

"I look forward to working as hard as I can as the Member for Londonderry and as Deputy Labor Leader in NSW to elect a Minns Labor Government in March."

She thanked her constituents for their support, saying "I will not forget it".

Ms Car returns to Labor's frontbench days after polls predicted Labor was on track to claim government for the first time since 2011.

The Newspoll showed NSW Labor had 40 per cent of the primary vote against the government on 35 per cent and was ahead on a two-party preferred basis, at 54 per cent to 46 per cent.

The Resolve Strategic poll showed Labor on 43 per cent of the primary vote, compared to 30 per cent for the coalition.

Australian Associated Press