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Blood-based tests for Cancer Screening
Context:
A multi-cancer early detection test can identify circulating tumour DNA or circulating tumour cells at an early stage, which can enhance the effectiveness of treatment.
Role of Cancer Screening
- Cancer accounts for 18% of deaths from noncommunicable diseases, making it the second leading cause of mortality in the country.
- In 2022 alone, India saw an estimated 14 lakh new cancer cases, with this number projected to increase by 12% by 2025.
- According to GLOBOCAN, breast, cervical, ovarian, and colorectal cancers are most prevalent among women, while men are more commonly affected by lung, esophageal, colorectal, and stomach cancers.
- According to the recent National Family Health Survey (NFHS-5, 2019-21), cancer screening in India is largely limited to cervical, breast, and oral cancers, with only 0.2-2% of the population having undergone any form of screening.
- The National Health Service in England aims to increase the proportion of people diagnosed at an early stage from 50% to 75% by 2028.
Blood-Based Tests
- Already a key component of annual preventive health check-ups, these tests can be adapted for cancer screening with high specificity and reasonable sensitivity at an affordable cost.
- A multi-cancer early detection (MCED) test, a type of liquid biopsy, identifies cancer signals—such as circulating tumour DNA (ctDNA) and circulating tumour cells (CTCs)—released by cancerous cells into the bloodstream at early stages, when treatment is most effective.
- If a signal is detected, the test can often locate the cancer, aiding doctors in planning the appropriate care pathway.
- The MCED test can detect up to 50 types of cancer, including those like ovarian, liver, stomach, pancreatic, and esophageal cancers, etc.
- However, it’s important to note that the MCED test differs from genetic testing, which identifies inherited genes that may increase cancer risk over a lifetime.
- The MCED test does not assess genetic predispositions or inherited genetic changes related to cancer.
- Currently, MCED tests have not been approved by the U.S. FDA and Indian CDSCO.
Downsides of MCED
- A major concern is the risk of false positives (50%), where the test indicates cancer even when none is present.
- However, combining traditional screening methods with an MCED test can significantly lower this rate.
- They carry risks of overdiagnosis and overtreatment, which can result in unnecessary physical, psychological, and financial burdens.
