Background & Objective:
India is experiencing rapid demographic and epidemiologic transitions, accompanied by a steady rise in cancer burden. While cancer transition, characterised by a shift from infectious related cancers to life style related cancers, has been well documented in many high-income countries, it remains, unclear whether similar transitionis underwayin India. Most existing studies rely on site-specific incidence rates and trends, which describe how individual cancers change over time but do not capture how cancer reconfigre relative to one another within the overall cancer burden. This study examines whether chnages in cancer patterns in urban india reflect a broader process of cancer transition and explore the nature of these emerging patterns. 
Data and Methods:
Using population based cancer registry data from Chennai registry in India (1982-2012), we analysed incidence patterns for nine common and largely preventable cancers such as the cancers of the breast, cervix, oral cavity, lung, colorectum, prostate, stomach, esophagus, and liver. Initial analyses used age-adjusted incidence rate and jointpoint regression to assess the temporal trends in individual cancer sites. To capture the cancer transition in relative terms, incidence data were subsequently analysed using Compositional Data Analysis (CoDA) approach. Descriptive measures including the centre, clr variances, and aitchison distnace were used to summarise the pattern. Internal temporal dynamics were formally assessed using compositional linear regression with time as predictor, followed by compositional piecewise trend filtering to detect structural breaks in cancer dominance trajectories. 
Results:
Jointpoint analyses showed increasing trends for lifestyle-and tobacco-related cancers and declining trends for infection related cancers, particularly cervix and stomach. Compositional regression demonstrated that time explained substantial compositional variability (R² = 53% for male and 63% for females), indicating systematic re-organisation of cancer compostion. Among males, oral cancer remained the leading site, with lung and colorectal gaining dominance and stomach and esophagus declining. Among females, breast replaced cervix as the leading cancer site in the early 2000s, alongside rising lung, and colorectal cancers. piecewise trend-filtering revealed distinct non-linear transition phases, particularly during the late 1980s and 1990s.
Conclusion:
This study demonstrated that cancer transition in India is best understood as a reorganisation of cancer compositiions rather than a collection of independent rate trends. By inrtoducing CoDA to cancer epidemiology, we provide a robust framework for identifiying dominance shifts, structural breaks, and system level transitions, with important implications for cancer control, screening priorities, and prevention strategies in rapidly transitioning populations.