The global incidence of thyroid cancer (TC) has increased significantly in recent decades. Traditionally, this trend has been attributed to overdiagnosis resulting from the widespread use of imaging and improved diagnostic techniques, but increasing evidence suggests that current epidemiological patterns may not be fully explained by diagnostic factors alone. Most importantly, increasing rates of larger and more advanced tumors have been reported in several populations. This narrative review discusses the evidence on possible drivers of rising TC incidence: obesity and metabolic dysfunction, environmental exposures such as air pollution, and endocrine-disrupting chemicals (EDCs) and ionizing radiation, as well as molecular and genetic mechanisms involved in thyroid carcinogenesis. The role of advances in diagnostics and their contribution to overdiagnosis are also discussed. Current available data support a multifactorial model with better detection coupled with changes in environmental, metabolic and biological risk factors. A better understanding of the relative contribution and interaction of these determinants may help refine diagnostic strategies, reduce unnecessary interventions, and improve the prevention and management of TC.

TLS are ectopic, non-encapsulated aggregates of immune cells that develop de novo in non-lymphoid tissues in response to persistent antigenic stimulation, and have emerged as clinically relevant features of many solid tumours. However, conventional TLS assessment based on presence/absence, density, or simplified maturation scales does not adequately explain why TLS are associated with favourable, neutral, or even adverse clinical outcomes across tumour types and treatment settings. In this review, we synthesize current biological, spatial, and clinical evidence and argue that TLS should be interpreted not as static histologic findings, but as functional immune niches shaped by three interacting axes: structural maturity, spatial localization, and functional immune context. We discuss how mature germinal centre-positive TLS often reflect coordinated B-cell–T-cell cooperation and sustained antigen-driven antitumour immunity, whereas partially organised or suppressive TLS may display transitional or immunoregulatory properties. On this basis, we propose a pragmatic, pathology-oriented conceptual framework that groups TLS into three simplified functional states: TLS-A, representing mature effector TLS with germinal centre activity; TLS-B, representing organised but incompletely matured or functionally intermediate TLS; and TLS-C, representing TLS dominated by regulatory or suppressive immune programs. We further place these states within recurrent tumour microenvironment archetypes and outline the rationale for a “functional TLS score” integrating histopathologic and molecular readouts. Rather than introducing a definitive biological taxonomy, this framework is intended as a translational model for harmonising TLS interpretation, refining biomarker development, and supporting future studies on prognosis, immunotherapy response, and standardised pathology reporting in solid tumours.

TLSs are ectopic, non-encapsulated aggregates of immune cells that develop de novo in non-lymphoid tissues in response to persistent antigenic stimulation and have emerged as clinically relevant features of many solid tumours. However, conventional TLS assessment based on presence/absence, density, or simplified maturation scales does not adequately explain why TLSs are associated with favourable, neutral, or even adverse clinical outcomes across tumour types and treatment settings. In this review, we synthesise the current biological, spatial, and clinical evidence and argue that TLSs should be interpreted not as static histologic findings but as functional immune niches shaped by three interacting axes: structural maturity, spatial localisation, and the functional immune context. We discuss how mature germinal centre-positive TLSs often reflect coordinated B-cell–T-cell cooperation and sustained antigen-driven anti-tumour immunity, whereas partially organised or suppressive TLSs may display transitional or immunoregulatory properties. On this basis, we propose a pragmatic, pathology-oriented conceptual framework that groups TLSs into three simplified functional states: TLS-A, representing mature effector TLSs with germinal centre activity; TLS-B, representing organised but incompletely matured or functionally intermediate TLSs; and TLS-C, representing TLSs dominated by regulatory or suppressive immune programs. We further place these states within recurrent tumour microenvironment archetypes and outline the rationale for a “proposed functional TLS score” integrating histopathologic and molecular readouts. Rather than introducing a definitive biological taxonomy, this framework is intended as a translational model for harmonising TLS interpretation, refining biomarker development, and supporting future studies on prognosis, immunotherapy response, and standardised pathology reporting in solid tumours. Because this framework is derived from a narrative synthesis of published evidence rather than from formal validation, it should be regarded as hypothesis-generating and requires prospective, tumour-specific validation before clinical implementation.