Aims: To examine the occurrence and prognostic significance of intratubular germ cell neoplasia (IGCN) and microinvasive germ cell tumour (MGCT) in tissue adjacent to testicular germ cell tumours (TGCT) in adults.
Methods and results: The study was based on two Danish studies of adult patients with stage I TGCT and included 255 patients. Of 106 patients with seminoma, 75 [71%, 95% confidence interval (CI) 61, 79] had IGCN without MGCT and nine (8%, CI 4, 15) had both IGCN and MGCT. Of 149 patients with non-seminoma, 62 (42%, CI 34, 50) had IGCN without MGCT, and 32 (22%, CI 15, 29) had both IGCN and MGCT. Non-seminomas with a seminoma component were more often associated with MGCT (23 of 54 testes, 43%, CI 29, 57) than were non-seminomas without this component (nine of 95 testes, 10%, CI 4, 17) (P < 0.000 05, Fisher's exact test). Relapse-free survival was not influenced by the concomitant presence of the two precursor stages in the testes (P = 0.36, and P = 0.19, log rank test, respectively).
Conclusions: MGCT was a relatively frequent finding in testes adjacent to a macroscopic TGCT. However, neither IGCN nor MGCT predicted relapse for patients with stage I TGCT.