Chemotherapy-induced multicellularity drives drug-tolerant persistence state in tumor cells

Multicellularity is a well-documented microbial response to stress, however its role as an adaptive survival strategy in cancer remains unresolved. Here we reveal that drug stress, such as paclitaxel treatment, enable rapidly (within 24-48 hours) and efficiently (∼20-40%) convert single mouse breast 4T1 cancer cells into clonal multicellular spheroids, ultimately generating multicellular masses. Notably, multicellularity is reversible: upon stress removal, most of them restore a unicellular lifestyle that quickly becomes dominant. This transient multicellular state shields cells from hostile niches, functions as a drug-tolerant persistence (DTP) reservoir, and fuels post-therapy relapse, revealing multicellularity as a facultative evolutionary pivot for fitness gain. Importantly, blocking primordial germ cell (PGC) specification suppresses the multicellularity transition. Our findings reveal that certain cancer cells enable adopt unicellular–multicellular life cycle through phenotypic plasticity, dynamically adapting to microenvironmental shifts to maximize fitness. This discovery reframes cancer evolution and the drug-tolerant persistence (DTP) state, highlighting multicellularity as an adaptive, stress-inducible survival strategy against therapy.