Multiple myeloma (MM) is a malignant neoplasm of clonal plasma cells predominantly affecting older adults, with a median diagnosis age around 70 years. However, a minority of cases occur in younger individuals and may exhibit distinct biological behavior, treatment responses, and outcomes compared to typical late-onset disease. Early-onset multiple myeloma (EO-MM), defined here as diagnosis at or before 49 years, is rare but relevant for clarifying etiologic heterogeneity, hereditary predisposition, and potential environmental or infectious triggers. Studying its global distribution may provide insights into genetic susceptibility, environmental exposures, healthcare access, and registry quality, guiding prevention and detection strategies.

To analyze the global incidence of EO-MM (ages 0-49) in 2022, stratified by country, continent, United Nations (UN) region, Human Development Index (HDI), and World Bank income classification, and to explore potential genetic, environmental, and socioeconomic factors in specific populations.

This is a descriptive epidemiological study based on data extracted from the Cancer Today platform of the International Agency for Research on Cancer (IARC), part of the World Health Organization (WHO). Incidence estimates for MM in individuals aged 0-49 years in 2022 were analyzed. The age-standardized rate (ASR, per 100,000 inhabitants) was used for comparisons. Stratifications were made by geographic (country, continent, and UN region), socioeconomic (HDI), and economic (World Bank income classification) parameters to identify patterns and disparities.

A total of 14,011 new cases were identified globally in 2022, with an ASR of 0.21 per 100,000. The highest national ASRs were observed in Barbados (0.80), Solomon Islands (0.64), the United States (0.63), and Guadeloupe (0.60). Twenty-one countries, mostly low-income, reported zero cases. North America had the highest continental ASR (0.62), followed by Oceania (0.39), Europe (0.30), Latin America (0.25), Africa (0.19), and Asia (0.17). Among UN regions, Australia-New Zealand (0.47) and Northern Europe (0.42) showed relatively high rates, while Western Africa (0.13), South-Eastern Asia (0.11), and Micronesia (0.00) had the lowest. By HDI, very high HDI countries exhibited an ASR of 0.34, compared to 0.20 in high, 0.17 in low, and 0.16 in medium HDI nations. Income level analysis revealed a gradient: high-income countries had the highest incidence (0.36), followed by upper-middle- (0.22), lower-middle- (0.16), and low-income (0.15) nations. Brazil reported 530 cases, with an ASR of 0.26, above both the global and South American (0.23) averages.

EO-MM accounts for a small proportion of myeloma cases worldwide but displays marked geographic and socioeconomic disparities. Higher ASRs in very high HDI and high-income regions likely reflect better diagnostic capacity and cancer registration, as well as possible differences in population risk profiles. Lower rates in parts of Africa and Asia may result from underdiagnosis, limited diagnostic infrastructure, and competing health priorities, whereas elevated incidence in certain small island states could relate to genetic isolation and environmental exposures, warranting targeted investigation. Strengthening surveillance systems, improving access to early diagnosis, and expanding research into genetic and environmental determinants are fundamental to reducing the global burden of EO-MM and addressing disparities.