Endoscopic treatment for early carcinoma in the gastrointestinal tract has in the meantime become evidence-based and has been incorporated into national and international guidelines [1–3]. However, endoscopic therapy in the upper GI tract is only indicated for lesions that are limited to the mucosa, or at most the very superficial submucosa. In the lower GI tract, the definition of carcinoma first starts with submucosal infiltration, while “mucosal carcinomas” are equivalent to high-grade dysplasia in terms of their biological behavior; the term “mucosal cancer” should therefore not be used clinically.
Generally, the endoscopic appearance here can already provide an initial, approximate assessment of the depth of infiltration (into the mucosa or beyond) and can guide the subsequent management. The Paris classification, based on earlier Japanese classifications, was developed to allow morphological classification of superficial lesions [4,5]. The Paris classification should therefore be regarded as a part of standard endoscopic terminology.
The Paris classification of early and/or superficial tumors in the GI tract was developed by an international consortium, in a two-stage process to date. Superficial or early neoplasias in the entire GI tract are primarily assessed on the basis of their endoscopic appearance and are defined as type 0 (for other types, see the endoscopic classification of advanced tumors); the “0” is usually omitted in clinical practice — for example, “type IIa” instead of “type 0-IIa.”
The figure from the relevant paper  provides diagrammatic representations of the different shapes of tumor:
Typ 0-I indicates elevated or polypoid forms, namely0-Ip Polypoid/pedunculated0-Is Polypoid/sessile, broad-based
Typ 0-II indicates flat or superficial forms, namely0-IIa Flat and elevated0-IIb Completely flat0-IIc Superficially depressedThese types often consist of mixed forms — e.g., type IIa+c = flat and elevated with a central depression.Typ 0-III indicates excavated forms, without any further subgrouping:0-III Excavated/ulcerated
Types II and III are also referred to as nonpolypoid forms, as distinct from type I.An overview of all the tumor types, including mixed forms, is shown below:
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