Routine Blood Work Clues
While standard blood tests like a complete blood count (CBC) aren't designed to diagnose cancer directly, they can offer vital indirect signals. Dr. R
Ranga Rao explains that significant deviations in white blood cell counts, whether unusually high or low, can be indicative of blood cancers like leukemia or lymphoma, prompting further investigation. Similarly, low hemoglobin levels might suggest anemia, which, in some instances, could be linked to underlying gastrointestinal tumors or conditions such as multiple myeloma. Abnormal platelet counts can also raise suspicion, particularly if the bone marrow is affected. However, these findings are merely starting points, acting as warning signs rather than definitive diagnoses. Dr. Shelly Mahajan emphasizes that many cancers remain asymptomatic and may not manifest in routine blood parameters, meaning normal results don't rule out cancer, and abnormal ones don't confirm it. All abnormal results necessitate targeted follow-up tests, including specialized blood studies, imaging, or a biopsy for confirmation.
Introducing MCED Tests
Multi-cancer early detection (MCED) tests represent a significant advancement, analyzing circulating tumor DNA and other molecular markers released into the bloodstream. These sophisticated tests employ genomic sequencing and algorithmic analysis to identify patterns indicative of cancer before symptoms emerge. Their primary allure lies in their broad scope, with some platforms capable of screening for over 50 different types of cancer, including those notoriously difficult to detect early, like pancreatic, liver, and ovarian cancers. Dr. Rao views MCEDs as a 'tremendous development' for oncology, especially for late-diagnosed cancers. However, it's crucial to understand their limitations: they are not diagnostic tools. A positive result signals the need for further investigation, such as imaging and other specialized tests, but does not confirm a cancer diagnosis. Conversely, a negative result doesn't entirely eliminate the possibility of very early-stage disease. Dr. P.K. Jayachandran elaborates that tests like the Galleri test detect circulating tumor DNA fragments, which are shed by disintegrating cancer cells. Advanced genomic techniques are then used to infer the organ of origin. While effective, their sensitivity is higher for advanced cancers than for early-stage ones, and they have not yet supplanted conventional screening methods.
MCED Test Reliability in 2026
As of 2026, current data indicate that many MCED tests boast high specificity, often exceeding 99%, which significantly minimizes the occurrence of false positives. Nevertheless, their sensitivity can fluctuate considerably based on the specific cancer type and its stage. Dr. Rao points out that performance varies across different platforms and cancer types, with sensitivity for early-stage diseases being a key area of variability that impacts their screening utility. Dr. Mahajan highlights the inherent challenge in laboratory medicine: achieving a balance between sensitivity and specificity. Traditional tumor markers, like CEA or CA-125, are not always cancer-specific and can be elevated due to benign conditions such as inflammation or cysts, potentially causing undue anxiety and leading to unnecessary investigations. Conversely, normal levels do not always guarantee the absence of disease. Dr. Jayachandran notes that while advanced blood tests are under clinical trials to detect pre-symptomatic cancer signals, they still require more robust research for definitive diagnostic validation. A biological hurdle is that early-stage cancers might 'shed' minimal tumor DNA, leading to normal-appearing blood test results even when a treatable tumor is present, offering a potentially false sense of security.
Blood Tests vs. Imaging & Biopsy
A singular blood test, even an advanced MCED, cannot replace the crucial role of imaging or biopsy in cancer detection. Dr. Mahajan stresses that imaging techniques like MRI, CT, and PET-CT scans are essential for pinpointing the location, size, and spread of suspicious lesions, providing vital anatomical context. However, even sophisticated imaging cannot identify a tumor's molecular subtype. For this definitive information, the 'gold standard' remains a biopsy, where microscopic examination of tissue confirms whether a tumor is benign or malignant. Therefore, blood investigations, including MCEDs, should be viewed as supplementary tools within a broader diagnostic framework. Dr. Jayachandran unequivocally states that no single blood test currently replaces the need for imaging and biopsies. While future advancements might introduce more comprehensive blood tests for cancer detection, imaging will likely remain indispensable for assessing the extent of the disease. Biopsy continues to be central to diagnosis, with blood tests serving as supportive evidence rather than replacements for tissue confirmation.
The Role of Liquid Biopsy
Liquid biopsy, a method that analyzes tumor-derived components circulating in the blood, is already integrated into cancer care in India, though primarily not as a mass screening tool. Dr. Jayachandran confirms its widespread use in cancer treatment for precision oncology therapies across various cancers, including colorectal, breast, stomach, and lung cancers. However, its current application is more focused on treatment decisions and prognostic assessment rather than initial diagnosis. It aids in guiding therapeutic strategies by identifying specific genetic mutations or biomarkers within the cancer cells found in the blood, allowing for more targeted and effective treatments, especially in managing advanced or recurrent disease. It's a powerful tool for personalized medicine but not yet a primary method for detecting cancer in the general population.
MCEDs for Population Screening?
Experts agree that MCED tests are not yet ready for widespread, routine population screening. Dr. Rao emphasizes the need for extensive long-term evidence demonstrating a clear impact on reducing cancer-related mortality. Ongoing research is critically evaluating not only detection rates but also patient outcomes, cost-effectiveness, and the most appropriate follow-up strategies for positive results. Regulatory bodies have not yet granted universal endorsement for their use in general screening. For now, Dr. Rao suggests a more targeted application, recommending MCEDs for individuals at higher risk, such as those with a strong family history of cancer or known genetic predispositions. Even in these cases, MCEDs should complement, not substitute, established screening methods like mammography or colonoscopy. Clinical guidelines are still under development, addressing key questions about test eligibility, interpretation of positive results, and measures to mitigate potential overdiagnosis and unnecessary interventions.
