A cancer diagnosis can leave lasting psychological scars akin to those inflicted by war, with the impact in some cases lasting for years, US researchers found in a study.

More than a decade after being told they had the disease, nearly four out of 10 cancer survivors said they were still plagued by symptoms of post-traumatic stress disorder, or PTSD, says lead researcher Sophia Smith from the Duke Cancer Institute in Durham, North Carolina.

Those symptoms included being extra jumpy, having disturbing thoughts about the cancer and its treatment, or feeling emotionally numb toward friends and family.

The study, published in the Journal of Clinical Oncology, is based on a survey of 566 patients with non-Hodgkin's lymphoma, a relatively common kind of cancer.

The new survey shows that low-income people are extra vulnerable to the psychological impact of living with cancer.