Which subtype has the shortest MRD lead time?

• A. Luminal A
• B. HER2-positive
• C. Triple-negative breast cancer
• D. Luminal B

Answer: (C)

MRD lead time is the period from when minimal residual disease is detected after initial therapy to the time a relapse becomes clinically evident. The subtype with the shortest lead time is the one that tends to behave most aggressively, with rapid growth of residual cancer cells and fewer long-lasting control options. Triple-negative breast cancer fits this pattern: it lacks hormone receptors and HER2, so there are fewer targeted therapies to slow any residual disease, and such tumors often relapse sooner after treatment compared with other subtypes.

Luminal A tumors are ER/PR positive and HER2 negative, usually low-grade with slow, late recurrences, so their MRD would take longer to progress to relapse. Luminal B is more aggressive than luminal A but still generally relapses later than triple-negative. HER2-positive cancers can be aggressive as well, but the availability of effective HER2-targeted therapies often delays relapse compared with triple-negative disease. Hence, the shortest MRD lead time is seen with triple-negative breast cancer.