Abstract Conventional histopathological classification is based on predefined disease categories, into which individual cases are assigned. However, biological phenomena are inherently continuous, and as diagnostic parameters increase, category-based classification systems inevitably give rise to numerous exceptions and borderline cases, reflecting a fundamental structural limitation. In this paper, we propose a conceptual framework in which tumours are not treated as discrete disease entities but are instead represented as points, or vectors, within a multidimensional coordinate space defined by mutually independent biological axes, such as the direction of differentiation, the degree of differentiation, and proliferative activity. Within this framework, so-called “special-type tumours” are understood not as independent disease units, but as clusters of points that share specific differentiation trajectories. By adopting this vector-based representation, diagnostic ambiguity and intratumoural heterogeneity can be interpreted not as diagnostic failures, but as structural properties intrinsic to tumour biology. Although the proposed framework is not intended to directly replace existing diagnostic systems, it aims to provide an organ-transcending theoretical backbone that supports more transparent and reproducible histopathological diagnosis, without being restricted to specific organs or tumour types.
Takako Okubo (Mon,) studied this question.