Mitogen-activated protein kinase (MAPK) cascades are key signalling pathways that regulate a wide variety of cellular processes, including proliferation, differentiation, apoptosis and stress responses. The MAPK pathway includes three main kinases, MAPK kinase kinase, MAPK kinase and MAPK, which activate and phosphorylate downstream proteins. The extracellular signal-regulated kinases ERK1 and ERK2 are evolutionarily conserved, ubiquitous serine-threonine kinases that regulate cellular signalling under both normal and pathological conditions. ERK expression is critical for development and their hyperactivation plays a major role in cancer development and progression. The Ras/Raf/MAPK (MEK)/ERK pathway is the most important signalling cascade among all MAPK signal transduction pathways, and plays a crucial role in the survival and development of tumour cells. The present review discusses recent studies on Ras and ERK pathway members. With respect to processes downstream of ERK activation, the role of ERK in tumour proliferation, invasion and metastasis is highlighted, and the role of the ERK/MAPK signalling pathway in tumour extracellular matrix degradation and tumour angiogenesis is emphasised. signalling elements that regulate basic processes including cell proliferation, differentiation and stress responses (1-3). These cascades transmit signals through sequential activation of three to five layers of protein kinases known as MAPK kinase kinase kinase (MAP4K), MAPK kinase kinase (MAP3K), MAPK kinase (MAPKK), MAPK and MAPK-activated protein kinases (MAPKAPK). The first three central layers are considered as a basic core unit, while the last two layers appear in some cascades and can vary among cells and stimuli. Four MAPK cascades have been defined based on the components in the MAPK layer: ERK1/2, c-Jun N-terminal kinase (JNK), p38 MAPK and ERK5. This review focuses on the ERK cascade (4-6) which involves several kinases in the MAP3K layer (mainly Rafs), including Ras/Raf/MAPK (MEK) 1/2 at the MAPKK layer, ERK1/2 at the MAPK layer and several MAPKAPKs in the next layer (ribosomal s6 kinases, MAP kinase-interacting serine/threonine-protein kinases, mitogen-and stress-activated protein kinases and cytosolic phospholipase A2). ERK cascades are highly regulated cascades that are responsible for basic cellular processes, including cell proliferation and differentiation. These regulatory factors affect bispecific phosphatases (7-10), scaffold proteins (11-14), signal duration and intensity (15), and the dynamic subcellular localization of cascade components (16,17). Due to the importance of the ERK cascade, ERK disorders are harmful to cells and ultimately to the body. Excessive activation of upstream proteins and kinases in the ERK pathway has been shown to induce various diseases, including cancer, inflammation, developmental disorders and neurological disorders (18-22). Since ERK1 and ERK2 are very similar, the singular form of ERK is used in this review, although two subtypes exist. Dysfunction in the Ras-ERK pat...