This study takes a unique and comprehensive approach to assess the inequality of gender's effect on mortalities' cancer in twenty-seven European Union (EU) countries in 2013-2021. It utilizes Pooled Ordinary Least Squares and Quantile Regression models to explore gender-specific variations in cancer mortality, identifying key factors and establishing connections between gender inequality indicators and mortality rates. The findings are not only significant but also intriguing, revealing the substantial influence of indicators like women's average years of schooling, contributing to a 55.0277 increase in women's cancer mortality. Conversely, Gross National Income per capita among women correlates with a -0.0003 reduction in women's cancer mortality. Lifestyle factors such as engagement in daily cooking/housework, avoidance of smoking/harmful drinking, and participation in physical activities/consumption of fruits and vegetables are associated with mortality reductions. In contrast, unmet medical examination needs, positive health perceptions, education/training, ministerial positions, assembly memberships, and leisure activities are linked to increased women's cancer mortality. The urgency of addressing healthcare gender gaps is underscored by these findings, guiding interventions, policies, and gender equity support in alignment with UN SDGs. This study uniquely focuses on the EU context, employing an interdisciplinary approach to explore mechanisms linking gender inequality and cancer mortality.