Maclean, Fiona

Aims Testicular sex cord‐stromal tumours (TSCSTs) are rare neoplasms that arise from (or show differentiation to) elements derived from the sex cords or intertubular stroma. The current classification (World Health Organization, 2022) is based almost entirely on morphology, with many tumour types such as granulosa cell tumours being defined based on their resemblance to ovarian counterparts. Recent studies have uncovered new clinicopathological, molecular and biological nuances within this group of tumours, underscoring differences with ovarian homologues. Methods and results Considering the new data, a group of genitourinary pathology experts (Testicular Sex Cord‐Stromal Tumour [TESST] group) has proposed a revised ‘TESST classification’ that incorporates the best available evidence. This classification is structured and hierarchical, composed of the following tiers: (1) group, (2) category, (3) entity and (4) histological pattern. ‘Group’ refers to the histological compartment a specific tumour belongs to (sex cords, stroma or both), whereas ‘category’ is defined by the phenotype of the tumour, taking non‐neoplastic elements of the ovary and testis as a reference. The third tier, ‘entity’, refers to neoplasms with shared clinicopathological and/or molecular features that justify classifying them as distinct types. Lastly, ‘histological patterns’ are recurrent morphological variations within entities that are not linked to distinct clinicopathological or molecular features. Conclusions We propose a classification that will provide a framework to improve current clinical management and guide future research in the field.

According to the current WHO classification, noninvasive germ cell neoplasia of the testis comprises germ cell neoplasia in situ (GCNIS), specific forms of intratubular germ cell neoplasia, and gonadoblastoma. Because type II germ cell tumors (GCT, type II) arise from GCNIS, accurate detection of precursor lesions is diagnostically important. In preparation for the 2024 International Society of Urological Pathology (ISUP) Consensus Conference on genitourinary precursor lesions, which took place in Florence, Italy, an anonymous survey was distributed to ISUP members to assess current diagnostic practices regarding testicular precursor lesions. The literature and current WHO classification affirm the significance of precursor lesions in testicular tumours. Working Group 4—Precursor Lesions of the Testis—focused on their practical application by individual pathologists rather than establishing consensus from scientific data. There is strong agreement that GCNIS is the preferred and appropriate term for GCT precursor lesions and that its presence should be reported in cases of invasive GCT. Respondents also agree that “seminoma with intratubular nonseminoma” is the appropriate terminology for seminoma with an associated noninvasive nonseminomatous (embryonal carcinoma, yolk sac tumor, trophoblasts, or teratoma) component. Most pathologists prefer to use OCT3/4 as the primary immunohistochemical marker, and a panel was generally not considered necessary. No consensus is reached regarding the requirement for immunohistochemistry to confirm GCT precursor lesions in the testis. Three questions remain open: the value of subtyping intratubular lesions, the immunohistochemical approach to gonadoblastoma, and the criteria distinguishing Sertoli cell nodules from Sertoli cell tumors.