The frequency of intratubular embryonal carcinoma: implications for the pathogenesis of germ cell tumours

Aims: To define the frequency and distribution of intratubular embryonal carcinoma (IEC) in an attempt to shed light on the pathogenesis of non‐seminomatous germ cell tumours (NSGCTs). Intratubular germ cell neoplasia of unclassified type (IGCNU) is common in NSGCT; however, IEC is rarely described. Methods and results: Sixty‐two germ cell tumours were reviewed. Immunochemistry for CD30, placental alkaline phosphatase (PLAP) and c‐kit was performed. The distribution, immunohistochemistry and morphology of the intratubular neoplasia were noted. All cases showed widespread IGCNU with PLAP and c‐kit staining. CD30 showed strong focal intratubular positivity in 20/31 NSGCTs, 1/29 seminomas and 1/4 mixed seminomas/NSGCTs. In 17 of these cases, the CD30+ tubules were not easily identified as IEC on routine stains. These tubules were scanty in number and c‐kit was negative, though some showed patchy PLAP staining. The cells within these tubules differed morphologically from IGCNU. Conclusions: IEC defined by CD30 positivity is not always easily identified on haematoxylin and eosin staining. We suggest that IEC is a common intermediate step between IGCNU and NSGCTs. The patchy and focal distribution of IEC suggests it may evolve quickly to invasive disease.