In oncology, a quiet revolution is reshaping how we classify cancer. It is not just about treatments or therapies; it is about the codes behind every diagnosis, claim, and policy decision.
This article explores the evolving behavior codes within the International Classification of Diseases for Oncology (ICD-O) and what these changes mean for insurers, particularly in critical illness (CI) products.
ICD codes are the foundation of modern healthcare data. They translate complex diagnoses into standardized formats, supporting billing, research, and care coordination. While ICD-10 has long been the global standard, ICD-11 now offers greater flexibility, integration, and specificity.
For cancer, however, ICD alone is not enough. ICD-O adds layers for morphology, behavior, and grading, offering a more detailed view of tumor biology and behavior.
The International Classification of Diseases for Oncology (ICD-O) was introduced by the World Health Organization (WHO) in 1976 as a specialized system for coding cancer registries. Unlike the broader ICD system, which classifies diseases generally, ICD-O captures the unique characteristics of tumors, including their topography (anatomical site), morphology (cell type), behavior, and grade.
Each update of ICD-O has mirrored the field’s shift from purely histological classification to integrated molecular and genetic insights. This evolution ensures more precise diagnosis, better treatment planning, and consistent data for epidemiology and insurance decision-making.
Behavior codes are at the core of the ICD-O system. These codes – /0 (benign), /1 (uncertain or borderline malignancy), /2 (in situ), and /3 (malignant) – are critical in defining tumor behavior. They help determine whether a tumor is likely to remain localized, invade surrounding tissues, or metastasize. In ICD-O-3.2, many of these codes were updated to reflect current clinical, molecular, and pathological knowledge.2
Tumors can move between categories based on emerging evidence. This is not a one-way progression.
A tumor once classified as malignant may be reclassified as borderline, while others previously considered benign may now be labeled malignant. These changes aim to improve diagnostic accuracy and clinical relevance.
Here are a few notable examples of behavior code transitions in ICD-O-3.2:
These shifts affect cancer registries, clinical decision-making, and insurance frameworks. For insurers, staying current with these changes is critical to ensuring accurate underwriting, fair claims adjudication, and sustainable product pricing.
The WHO Blue Books, also known as the WHO Classification of Tumors, are authoritative guides that define and categorize tumors based on the latest consensus in pathology. They reflect both histological and molecular features and are updated regularly by subject matter experts. These volumes often introduce new tumor types, revised terminology, and behavior classifications before those changes are incorporated into ICD-O coding.4
This timing gap can create challenges for insurers. A pathology report may use a new Blue Book term that does not correspond with any existing ICD-O code, making it unclear whether the diagnosis qualifies under a policy’s cancer definition. This can lead to confusion, inconsistent claims decisions, or disputes between insurers and policyholders.
To close this gap, insurers should implement a clinical review process that incorporates both ICD-O and the most recent WHO Blue Book guidance. Maintaining a reference table that maps new terminology to existing ICD-O codes, along with interim interpretations, supports consistent, medically aligned claims and underwriting decisions.
Cancer accounts for 50% to 70%5 of CI claims. A change in how tumors are classified – particularly behavior code shifts in ICD-O – can significantly impact the claims landscape. A tumor previously coded as benign or borderline may now qualify as malignant, making it eligible for a cancer claim under existing CI definitions. For example, pancreatic neuroendocrine tumors (PanNETs), once considered benign, are now classified as malignant under ICD-O-3.2. Claims that were previously denied may now be payable.
These reclassifications also affect underwriting. Tumors once seen as low-risk and accepted at standard rates may now require exclusions, loadings, or declines. Pituitary neuroendocrine tumors (PitNETs) once classified as benign and often discovered incidentally, are now coded as malignant. This shift requires a review of underwriting guidelines.
Pricing is also impacted. While short-term effects may appear modest, the cumulative impact over time could be substantial – particularly in markets with high screening rates for certain gastrointestinal cancers, such as Japan and South Korea. Earlier detection in these regions may lead to more claims for tumors now classified as malignant but historically considered benign and excluded. Insurers must reassess definitions, update guidelines, and refine pricing to align with evolving classifications.
Under ICD-O-3.2, all neuroendocrine tumors (NETs) are now classified as malignant (/3), regardless of grade or anatomical site. This includes both well-differentiated NETs, which grow slowly and often have favorable outcomes, and poorly differentiated neuroendocrine carcinomas (NECs), which are more aggressive and linked to worse prognoses. The Ki-67 index, a marker of cellular proliferation, is used to grade these tumors. Even low-grade NETs (G1 and G2) now carry a malignant classification, reflecting the growing view that all NETs present some risk of recurrence or metastasis.6
A notable example is the reclassification of pituitary adenomas as PitNETs, which are now coded as malignant (/3).7 Although this change aligns with the WHO Blue Books, it remains a subject of debate. Most pituitary adenomas are clinically benign, slow-growing, and often discovered incidentally. Only a small portion demonstrate invasive behavior. Despite this, the new classification seeks to standardize terminology across neuroendocrine tumors.
Insurance impact: Reclassifying all NETs, including PitNETs, as malignant has major implications for critical illness (CI) insurance. These tumors may now qualify for claims, even if low-grade or asymptomatic. Insurers should reassess policy wording, particularly exclusions for non-metastatic or low-risk tumors, and consider updates to underwriting guidelines. Increased claims volume is possible, making it important to ensure consistent and medically informed adjudication practices.
Thymomas are rare tumors that originate from the epithelial cells of the thymus, typically affecting individuals between ages 40 and 60. Many thymomas are indolent and discovered incidentally. Under ICD-O-3.2, they are now classified as malignant (/3), reflecting their potential for local invasion and, in some cases, metastasis. This reclassification aligns with updated pathological insights, although early-stage types – A, AB, and B1 – have excellent survival outcomes.8
Insurance impact: This malignant reclassification of thymomas may now qualify for CI claims under cancer definitions. Insurers should review exclusions for early-stage thymomas and update underwriting criteria to reflect their variable behavior and favorable early-stage prognosis.
GISTs arise from the interstitial cells of Cajal in the gastrointestinal tract. Previously, they were variably classified as benign, borderline, or malignant based on tumor size and mitotic rate. ICD-O-3.2 now uniformly classifies all GISTs as malignant (/3). While many small GISTs with low mitotic activity are clinically indolent, the reclassification reflects their potential for recurrence and metastasis, particularly in larger or higher-grade cases.9
Insurance impact: In countries like Japan and Korea, routine screening may increase early-stage GIST detection. This could lead to more CI claims for tumors that were historically excluded. To manage this, insurers may need to introduce exclusions for early-stage or low-risk GISTs or adopt tiered definitions that consider tumor size and mitotic index. In markets without routine screening, the impact may be smaller but still warrants attention.
The evolution of cancer classification codes is not just a clinical shift – it carries significant operational and financial implications for the insurance industry. To stay aligned with medical advances and maintain sustainability, insurers should take the following strategic actions:
The reclassification of cancer behavior codes reflects meaningful progress in medical science. Our understanding of tumor biology has advanced significantly over the past decade, but it brings complexity and greater responsibility. For insurers, the challenge is to keep pace with these changes while maintaining clarity, fairness, and sustainability in product design, underwriting, and claim management. These changes may seem technical or minor, but their impact on insurance operations is significant.
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