This study investigates the senescence-like cell cycle arrest in human naevi (moles) associated with BRAF $ ^{E600} $ mutations. Human naevi are benign melanocytic tumors that frequently carry the BRAF $ ^{E600} $ mutation, a key oncogenic driver. Despite this mutation, naevi typically remain in a growth-arrested state for decades and rarely progress to melanoma. The study shows that sustained BRAF $ ^{E600} $ expression in human melanocytes induces cell cycle arrest, accompanied by the induction of p16 $ ^{INK4a} $ and senescence-associated acidic β-galactosidase (SA-β-Gal) activity, a common senescence marker. In vivo, congenital naevi are invariably positive for SA-β-Gal, indicating the presence of this marker in growth-arrested, neoplastic human lesions. In growth-arrested melanocytes, both in vitro and in situ, there is a marked mosaic induction of p16 $ ^{INK4a} $ , suggesting that factors other than p16 $ ^{INK4a} $ contribute to protection against BRAF $ ^{E600} $ -driven proliferation. Naevi do not appear to suffer from telomere attrition, arguing in favor of an active oncogene-driven senescence process rather than a loss of replicative potential. Thus, both in vitro and in vivo, BRAF $ ^{E600} $ -expressing melanocytes display classical hallmarks of senescence, suggesting that oncogene-induced senescence represents a genuine protective physiological process. The study also shows that BRAF $ ^{E600} $ induces senescence-like cell cycle arrest in normal human fibroblasts in a p16 $ ^{INK4a} $ -independent manner. Furthermore, human naevi display the hallmarks of senescent cells, including stable growth arrest, heterogeneous induction of p16 $ ^{INK4a} $ and SA-β-Gal activity. The study also shows that there is no apparent telomere loss in naevi, arguing in favor of an active oncogene-driven senescence process rather than senescence triggered by exhaustion of replicative potential. The findings suggest that oncogene-induced senescence is a physiological mechanism that limits the progression of premalignant lesions.This study investigates the senescence-like cell cycle arrest in human naevi (moles) associated with BRAF $ ^{E600} $ mutations. Human naevi are benign melanocytic tumors that frequently carry the BRAF $ ^{E600} $ mutation, a key oncogenic driver. Despite this mutation, naevi typically remain in a growth-arrested state for decades and rarely progress to melanoma. The study shows that sustained BRAF $ ^{E600} $ expression in human melanocytes induces cell cycle arrest, accompanied by the induction of p16 $ ^{INK4a} $ and senescence-associated acidic β-galactosidase (SA-β-Gal) activity, a common senescence marker. In vivo, congenital naevi are invariably positive for SA-β-Gal, indicating the presence of this marker in growth-arrested, neoplastic human lesions. In growth-arrested melanocytes, both in vitro and in situ, there is a marked mosaic induction of p16 $ ^{INK4a} $ , suggesting that factors other than p16 $ ^{INK4a} $ contribute to protection against BRAF $ ^{E600} $ -driven proliferation. Naevi do not appear to suffer from telomere attrition, arguing in favor of an active oncogene-driven senescence process rather than a loss of replicative potential. Thus, both in vitro and in vivo, BRAF $ ^{E600} $ -expressing melanocytes display classical hallmarks of senescence, suggesting that oncogene-induced senescence represents a genuine protective physiological process. The study also shows that BRAF $ ^{E600} $ induces senescence-like cell cycle arrest in normal human fibroblasts in a p16 $ ^{INK4a} $ -independent manner. Furthermore, human naevi display the hallmarks of senescent cells, including stable growth arrest, heterogeneous induction of p16 $ ^{INK4a} $ and SA-β-Gal activity. The study also shows that there is no apparent telomere loss in naevi, arguing in favor of an active oncogene-driven senescence process rather than senescence triggered by exhaustion of replicative potential. The findings suggest that oncogene-induced senescence is a physiological mechanism that limits the progression of premalignant lesions.