A teratoma with both mature elements from all 3 germ-cell layers (ectodermal, mesodermal, and endodermal), and immature (embryonic, not foetal) tissues, most commonly of neural origin, consisting of primitive neurotubules, neuroepithelial rosettes, immature glial elements, immature ependyma, primitive muscle.
Relatively good if under age 15; guarded if adult (see table).
Grade, Immature teratoma
I) ≤ 1 focus/slide contains immature tissue—low-grade.
II) 2–3 foci contains immature tissue—high-grade, adjuvant radiation therapy; survival possible.
III) 4+ foci contains immature tissue—high-grade, adjuvant radiation therapy; prognosis very poor.
Based on any immature tissue on any 1 slide at 40X (low-power field).
Immature teratomas behave differently in children; grading is unnecessary, the only histological predictor of recurrence is the presence of foci of yolk-sac tumour (confirmed by IHC stains for CK, AFP, glypican 3, SALL4); immature neural tissue does not indicate malignancy in immature teratomas of infants as it does in adults.