New Delhi, March 22 : While radiotherapy is a highly effective cancer treatment -- useful for about 60 per cent of all cancers -- it may lead to residual cancer that has the potential to hide behind clear scans and lead to worse outcomes, according to a study.

Residual cancer is microscopic levels of cancer cells that are left behind after cancer treatments. These are often not visible on scan images, which can be misleading, argued researchers from the University of Chicago Medical Center in the US.

In an editorial, published in the journal Oncotarget, they said that this 'residual disease' is more common than expected and is linked to worse long-term outcomes.

'Residual cancer is identified on histology in 40 per cent of the lung, 57-69 per cent of renal cell, 7.7-47.6 per cent of prostate, and 0-86.7 per cent of hepatocellular carcinoma,' Dr. Muzamil Arshad from the varsity.

The expert called 'for a rethinking of how treatment success is judged and how cancer is followed up after therapy'.

Radiotherapy -- especially a form known as stereotactic ablative radiotherapy (SABR) -- is widely used to treat cancers in the lung, liver, prostate, and other organs.

SABR delivers high-dose radiation with outstanding precision and often shows excellent results on scans.

However, the team highlights that relying only on imaging may not provide a complete picture. Months or even years later, follow-up biopsies frequently reveal cancer cells that scan imaging tests were unable to identify.

The gap between what scans show and what tissue analysis finds can have serious consequences.

Studies across several cancer types have shown that patients with residual disease -- even if small -- are more likely to experience cancer recurrence and shorter survival. This pattern holds for rectal, cervical, prostate, and liver cancers, among others.

In some cases, not destroying the tumour completely may allow it to spread to distant organs.

"A complete response on scan imaging does not necessarily indicate the complete disappearance of the tumour. This mismatch can mislead both clinicians and patients into thinking treatment was more successful than it truly was,' said the editorial.

It encouraged more regular use of biopsy-based tests and new strategies to increase true effectiveness.

/IANS