This edition examines companion diagnostics (CDx) as they move from a regulatory checkbox to a strategic pillar of precision drug development. The FDA now lists 168 biomarker-drug pairings linked to approved diagnostic tests, and the CDx market is projected to grow from $9.37B in 2026 to $28.75B by 2035, a 13.3% CAGR, as targeted therapies and biomarker-defined patient populations expand. Broader molecular profiling NGS, comprehensive genomic profiling, and multiplex platforms is replacing sequential single-marker testing, while liquid biopsy, MRD monitoring, AI-assisted diagnostics, and decentralized testing are emerging as the next wave of applications.

Regulators on both sides of the Atlantic are reshaping the pathway to market. FDA and EMA policy shifts between 2024 and 2026 including a proposed Class III-to-Class II reclassification for eligible oncology nucleic acid-based CDx and updated EMA consultation guidance are aimed at streamlining development without loosening safety and effectiveness standards.

Despite this momentum, adoption still depends on closing evidence, access, and implementation gaps. Regulatory approval does not guarantee reimbursement, real-world payer denials show that clinical utility and medical necessity, not FDA clearance alone ultimately determine patient access, and coverage disparities remain especially pronounced outside the US.

Looking ahead, CDx is evolving toward longitudinal, AI-enabled, multi-analyte testing. Scale, partnerships, and evidence generation are becoming the key competitive differentiators, favoring  integrated pharma-diagnostic ecosystems and established platform players such as Foundation Medicine and Guardant Health over smaller, single-product entrants.