Lifetime cancer risk characterization of ambient PM-bound carcinogenic metals and polycyclic aromatic hydrocarbons (PAHs) were examined in the cities of Los Angeles (USA), Thessaloniki (Greece) and Milan (Italy), which share similar Mediterranean climates but are different in their urban emission sources and governing air quality regulations. The samples in Milan and Thessaloniki were mostly dominated by biomass burning activities whereas the particles collected in Los Angeles were primary impacted by traffic emissions. We analyzed the ambient PM2.5 mass concentration of Cadmium (Cd), Hexavalent Chromium (Cr(VI)), Nickel (Ni), Lead (Pb), as well as 13 PAH compounds in the PM samples, collected during both cold and warm periods at each location. The Pb exhibited the highest annual-average concentration in all 3 cities, followed by Ni, As, Cr(VI), Cd and PAHs, respectively. The cancer risk assessment based on outdoor pollutants was performed based on three different scenarios, with each scenario corresponding to a different level of infiltration of outdoor pollutants into the indoor environment. Thessaloniki exhibited rather high risk value associated with lifetime inhalation of As, Cr(VI) and PAHs. The highest cancer risk values were calculated in Milan where the lifetime risk of exposure to As, Cr(VI) and PAHs exceeded the US EPA standard across all scenarios by a considerable margin. The risk associated with Cr(VI) in Milan, which was the most significant among the investigated elements, ranged from (6.08±0.36)×10-6 to (9.82±0.58) ×10-6. In contrast, the estimated risks associated with metal and PAHs in Los Angeles were mostly comparable to the guideline value, even when the infiltration factor was assumed to be at peak. This observation highlights the impact of local air quality measures in improving the air quality and lowering the cancer risks in Los Angeles compared to the other two cities.