Hidden Residual Cancer Behind Clear Scans Linked to Worse Prognosis: Study

New Delhi: While radiotherapy remains one of the most effective cancer treatments—benefiting approximately 60% of cancer patients—a new study warns that microscopic residual cancer may linger undetected, potentially leading to poorer long-term outcomes. Researchers from the University of Chicago Medical Center highlighted the issue in an editorial published in the journal Oncotarget.

Residual cancer refers to tiny clusters of cancer cells left behind following treatment, often invisible on standard imaging scans. The study emphasizes that while scans may suggest complete tumor resolution, they may not reveal these hidden cells, posing a risk for recurrence and worse prognosis.

“Residual cancer is histologically present in 40% of lung, 57-69% of renal cell, 7.7-47.6% of prostate, and up to 86.7% of hepatocellular carcinoma cases,” noted Dr. Muzamil Arshad, one of the lead authors. This indicates residual disease is far more common than previously assumed.

The editorial particularly focuses on stereotactic ablative radiotherapy (SABR), a high-precision, high-dose radiation therapy commonly used to treat cancers in organs like the lung, liver, and prostate. Although SABR typically produces excellent imaging results, the researchers caution against over-relying on scan findings to declare treatment success.

Months or even years after apparently successful radiotherapy, follow-up biopsies often reveal lingering cancer cells undetected by imaging. This discrepancy between scan results and tissue analysis can mislead both doctors and patients, fostering false confidence in the treatment outcome.

Evidence across multiple cancer types, including rectal, cervical, prostate, and liver cancers, shows that patients with residual disease—even at microscopic levels—face a higher risk of recurrence and reduced survival rates. In some cases, incomplete eradication may also facilitate metastasis to distant organs.

The researchers argue for a shift in how post-treatment success is evaluated, suggesting that more routine use of biopsy-based assessments and innovative therapeutic strategies are necessary to address residual disease effectively.

“A clear scan does not always equate to complete tumor elimination,” the authors stressed, urging oncologists to adopt a more vigilant follow-up approach to improve long-term patient outcomes.