A Malaysian researcher has raised concern PTSD may be going undiagnosed in cancer survivors.

Post-traumatic stress disorder (PTSD) in cancer patients may be much higher than previously thought, research suggests.

A Malaysian study of nearly 500 patients published in journal CANCER found 22 per cent had partial or full PTSD six months after diagnosis.

One third were still living with PTSD at four years.

The study also found that, compared with patients with other cancer types, those with breast cancer were 3.7 times less likely to develop PTSD at six months but not at four years.

The findings highlight the need for early identification, careful monitoring and treatment of PTSD in cancer survivors, say the researchers.

They did however note that the results may not apply to non-Asian populations.

Although PTSD is primarily known to develop in individuals following a traumatic event such as a serious accident, natural disaster or war, it can also occur in patients diagnosed with cancer.

Dr Caryn Mei Hsien Chan at the National University of Malaysia says patients must be told seeking help to manage the emotional upheaval of a cancer diagnosis is okay.

"Many cancer patients believe they need to adopt a 'warrior mentality' and remain positive and optimistic from diagnosis through treatment to stand a better chance of beating their cancer," Dr Chan said.

"To these patients, seeking help for the emotional issues they face is akin to admitting weakness."

Many survivors also live in fear their cancer may come back adding to their psychological stress.

Because of this, survivors might skip visits to their oncologists or other physicians to avoid triggering memories of their past cancer experience.

Dr Chan warned this could lead to delays in seeking help for new symptoms or even refusal of treatment for unrelated conditions.

"We need psychological evaluation and support services for patients with cancer at an initial stage and at continued follows-up because psychological well-being and mental health, and by extension, quality of life, are just as important as physical health," she said.