Yoji Wani Department of Pathology, Kurashiki Central Hospital, Kurashiki, Japan 1. Houghton O, Connolly LE, McCluggage WG. Morules in endo- metrioid proliferations of the uterus and ovary consistently express the intestinal transcription factor CDX2. Histopathology 2008; 53; 156–165. 2. Wani Y, Notohara K, Saegusa M et al. Aberrant Cdx2 expression in endometrial lesions with squamous differentiation: important role of Cdx2 in squamous morula formation. Hum. Pathol. 2008; 39; 1072–1079. 3. Saegusa M, Hashimura M, Kuwata T et al. A functional role of Cdx2 in beta-catenin signaling during transdifferentiation in endometrial carcinomas. Carcinogenesis 2007; 28; 1885– 1892. 4. Nakatani Y, Masudo K, Nozawa A et al. Biotin-rich, optically clear nuclei express estrogen receptor-beta: tumors with morules may develop under the influence of estrogen and aberrant beta-catenin expression. Hum. Pathol. 2004; 35; 869–874. Uterine and extrauterine plexiform tumourlets are sex-cord-like tumours with myoid features DOI: 10.1111/j.1365-2559.2009.03234.x Sir: Uterine tumours resembling ovarian sex cord tumours 1 (UTROSCT) are neoplasms related to endo- metrial stroma that mimic ovarian sex cord stromal tumours. Immunohistochemically, they have a com- plex polyphenotype that often coexpresses myoid, epithelial and sex cord markers. 2 Uterine plexiform tumourlets (UPT) are minute neoplasms 3 measuring <10 mm and are considered to be distinctive tumours of undetermined origin, but with myoid differentiation. 3,4 In order to review the concept of UPT, challenge their nomenclature and compare their morphology and immunohistochemistry with UTROSCT, we studied seven UPTs. Due to their small size, only three cases produced enough tissue for immunohistochemistry, the antibodies for which are shown in Table 1. Clinicopathologically, all lesions were incidental findings with sizes ranging from 1 to 9 mm. They originated from the endometrial stroma and were situated at the endomyometrial interface (Figure 1A) (cases 4, 6 and 7), in adenomyosis (Figure 1B) (cases 1 and 5), in the stroma of ovarian endometriosis in case 3 (Figure 1C,D) and in an endometrial polyp (Figure 1E) (case 2). Lesions were solitary in all cases except one, in which there were multiple foci of adenomyosis. They were nodular and well circumscribed in two cases (Figure 1A,C), but had irregular borders in four, where they extended into the myometrial fascicles (Figure 1F) or within the stroma of an endometrial polyp (Figure 1E) (case 2). Tumours grew in branching and anastomosing cords, separated by hyalinized stroma (Figure 1B,D,E) that merged, in case 7, with large foam cells similar to luteinized ovarian stromal cells (Figure 1F). The trabeculae had regular uniform epithelioid cells with eosinophilic or clear cytoplasm and oval nuclei. Mild mitotic activity was found only in case 2. Their clinicopathological data are summarized in Table 2. The three cases available for immunohistochemistry had a common immunophenotype coexpressing myoid markers such as smooth muscle actin and desmin (Figure 2A,B) and CD56 (Figure 2D,E). The CD10) trabeculae and cords originated from the endometrial stromal cuffs surrounding glands (Figure 2C). CAM5.2 was focally positive (Figure 2F). Both oestrogen and progesterone receptors were positive. Vimentin was negative in case 1. a-Inhibin (a-INH), calretinin (CLR), cytokeratin 7 and epithelial membrane antigen (EMA) were negative. Immunohistochemical results are shown in Table 3. The descriptive term UPT was coined in 1965 5 to replace previous terms such as endometrial glomus tumour or solid angioma. Electron microscopical 3,6 and Table 1. Antibodies Antibody Clone Dilution SMA HHF35 Diluted Desmin ZC18 Diluted H-caldesmon TD107 Diluted CD56 56C04 Diluted CD10 56C6, Diluted Calretinin 8P13 Diluted a-Inhibin R1 Diluted CAM5.2 CAM 5.2 Diluted Cytokeratin 7 OVTL-12 ⁄ 30 Diluted Epithelial membrane antigen ZCE113 Diluted Oestrogen receptor SP1 Diluted Progesterone receptor SP2 Diluted Vimentin SP20 Diluted Antibodies supplied by Master Diagnostica, Granada, Spain. Correspondence 497 Ó 2009 The Authors. Journal compilation Ó 2009 Blackwell Publishing Ltd, Histopathology, 54, 494–512.