Germ cell neoplasia in situ (GCNIS) with microinvasion. The interstitium shows scattered clusters of atypical germ cells (lower right corner) morphologically similar to those seen in the tubules. The tubular basement membrane is thickened. The interstitium also contains clusters of Leydig cells. The appearance of GCNIS is same regardless of the type of invasive germ cell tumor present in the testis. The incidence of GCNIS is lower for mature teratoma. GCNIS does not occur in prepubertal patients except for those with disorders of sex development. Children with conditions that increase the risk for germ cell tumors (cryptorchidism, gonadal dysgenesis, Down syndrome, undervirilization syndrome) may show germ cells with delayed maturation that can look like GCNIS.