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The Promise of Cancer Screening: Screen for Cancers Where Lives Can be Saved

Power of Ideas
The Promise of Cancer Screening: Screen for Cancers Where Lives Can be Saved

Innovations in cancer therapeutics and precision diagnostics impact countless lives as more and more cancer patients are able to claim the title of cancer survivor. While we applaud this progress, for too many patients innovation has not won out over disease. To reduce cancer—specific mortality and effectively improve population health, we need to expand efforts to detect the cancers most likely to be cured through early intervention.

Preventive health guidelines strongly recommend screening asymptomatic individuals for only four cancers (breast, cervix, colorectal, and lung) where population screening is relatively safe, accurate, and has a positive impact on public health. The recommended screening methodologies, while effective, are fragmented, which makes implementation, tracking, and execution in the healthcare system complicated and dependent on cumbersome patient follow-through. Consequently, guideline compliance remains well below desired levels. For example, compliance with screening guidelines for colorectal cancer—the second cause of US cancer deaths—remains stubbornly at 66 percent of eligible subjects in a disease where screening reduces the risk of death by 62 percent. Similarly, screening for lung cancer—the leading cause of US cancer-related death—demonstrates gross under-utilization, as only about 14 percent of persons eligible for screening are up to date with screening recommendations (i.e., were screened in the previous 12 months).

A screening paradigm using a blood-based test (referred to as a liquid biopsy) has the potential to improve compliance with cancer screening on a global, public health scale. Blood-based screening is simple, reduces the need for patient follow-through, is much easier to integrate into health-system workflows, and could expand accessibility to underserved communities and help close the screening gap.

We need to expand efforts to detect the cancers most likely to be cured through early intervention.

Blood-based screening tests have the potential for earlier detection of other cancer types when compared to current standard of care. The evidence-based screening guideline recommendations are based on the net population health benefit of early detection versus potential harm from unnecessary screening and follow-on diagnostic procedures. Consequently, the current guidelines recommend against screening for three other cancers in average-risk individuals—ovary, pancreas, and thyroid—noting that there is no net population benefit of screening or that the harms of unnecessary screening outweigh the benefits.

The complexities of malignant disease, the imperfect nature of screening tests, and the morbidity associated with follow-on diagnostics mean that early detection does not intrinsically confer net health benefit for all cancer types. For instance, a large study showed that while it was possible to find ovarian cancer early, the long-term outcomes sadly were no different for cancers detected early versus later. There is evidence that for some cancers, early intervention may result in significant harm. In prostate cancer, for example, it has been shown that some men can be successfully monitored with no treatment and no adverse long-term outcomes, whereas aggressive early surgery can lead to long-term negative health effects. In some hematologic malignancies, such as chronic lymphocytic leukemia, early chemotherapy confers no survival benefit to patients diagnosed in the early stages, and may introduce significant psychological and even financial distress for a condition in which no treatment is required.

Evidence-based assessments of population-level risk-benefit of cancer screening should guide the development of blood-based screening. At Guardant Health our focus is the development of a highly accurate blood test to screen for cancers where early detection can offer net population health benefit. Our corporate belief is that highly sensitive blood-based screening may provide net population health benefit in cancer types outside current guidelines, such as liver and bladder cancers, and in population groups at higher risk for certain cancers, such as pancreatic cancer. Clinical studies will be required to generate evidence for efficacy before screening tests can be offered at scale.

Reducing cancer mortality demands a thoughtful, evidence-driven approach to cancer screening. Some investigators have applied blood-based screening—even low-sensitivity tests—in a shotgun approach regardless of cancer type, with the presumption that early detection is always positive. In contrast, our approach is to use game-changing blood-based screening tools only when early detection has been demonstrated to be effective and beneficial. The promise of blood-based cancer screening is quickly becoming a reality and we see a brighter future for humanity by improving population health and reducing the harms of cancer.