Yolk sac tumour

Yolk sac tumour
Diagnosis in short
Yolk sac tumour. H&E stain.
LM	Schiller-Duval bodies (glomerulerus-like structures), variable architecture - usually reticular or microcystic
LM DDx	embryonal carcinoma, mixed germ cell tumour
IHC	AFP +ve, glypican 3 +ve, OCT3 -ve, CK19 +ve
Gross	white/yellow mucinous infiltrative mass
Grossing notes	orchiectomy grossing
Staging	testicular cancer staging
Site	testis, other
Prevalence	rare
Blood work	alpha-fetoprotein (AFP) elevated
Prognosis	poor
Clin. DDx	other germ cell tumours

Yolk sac tumour is an uncommon germ cell tumour that primarily afflicts infants and young boys.

It may be seen as part of mixed germ cell tumour. It is abbreviated YST.

It may be referred to as endodermal sinus tumour.

General

• Rare in pure form.
• Aggressive - especially extragonadal tumours.

Epidemiology:

• Most common GCT in infants and young boys.
• Bimodal age distribution:
  • <4 years.
  • 10-30 years.

Clinical:

• Elevated AFP.

Gross

• White/yellow mucinous infiltrative mass.

Microscopic

Classic feature:

• Schiller-Duval bodies.
  • Look like glomerulus - central blood vessel surrounded by epithelial-like cells a space and more epithelial-like cells
• Architecure - variable.
  1. Reticular - most common according to WMSP.
  2. Microcystic.
     • Lace-like pattern.
  3. Endodermal sinus-like - has Schiller-Duval bodies.
  4. Solid.
  5. Papillary.
  6. Glandular.
  7. Alveolar.
  8. Enteric.
  9. Polyvesicular vitelline.
  10. Hepatoid.
• +/-Eosinophilic hyaline globules (contain alpha-fetoprotein).

Notes:

• Has a loose stroma/vaguely discohesive -- unlike embryonal carcinoma.
• How to remember patterns REMember PlS GAP EH (or REM PS GAPEH) = reticular, endodermal sinus, microcystic, papillary, solid, glandular, alveolar, polyvesicular vitelline, enteric, hepatoid.
• Yolk sac tumours in adults are essentially always a component of a mixed germ cell tumour, i.e. if one sees a pure yolk sac tumour in an adult, it is probably under sampled.

Variants:

• Hepatoid pattern.
  • Vaguely resembles liver.
    • Hyaline globules (light red well-circumscribed globs).
    • Bile canaculi.
• Solid pattern.
  • Vaguely resembles seminoma.

DDx:

• Embryonal carcinoma - more nuclear atypia, nuclei usually overlap and classically vesicular.
• Mixed germ cell tumour.

Images

Case 1

• 

  Yolk sac tumour. (WC/Nephron)

Case 2

• 

  YST with hyaline bodies - intermed. mag. (WC)

• 

  YST with hyaline bodies - high mag. (WC)

• 

  YST with hyaline bodies - very high mag. (WC)

Case 3

• 

  YST - low mag. (WC)

• 

  YST - intermed. mag. (WC)

• 

  YST - high mag. (WC)

• 

  YST - very high mag. (WC)

www images

• Hepatoid Pattern (webpathology.com).
• Schiller-Duval body (webpathology.com).
• Hyaline globules (webpathology.com).
• Yolk sac tumour - case 1 - several images (upmc.edu).
• Yolk sac tumour - case 2 - several images (upmc.edu).
• Testicular germ cell tumours (moffitt.org).

IHC

ISUP consensus paper by Ulbright et al.:

• OCT3 -ve.
  • Positive in seminoma and embryonal carcinoma.
• Alpha-fetoprotein (abbreviated AFP) +ve.
• Glypican 3 +ve.
  • More sensitive than AFP.
• CD117 +ve (~60% +ve in a series of 52 solid YSTs).

Others:

• CK19 +ve.
  • Seminoma -ve, embryonal carcinoma -ve, GCNIS (ITGCN) -ve, normal testis -ve.
• Cytokeratin +ve.^{[citation needed]}
• CD30 -ve.
  • Positive in embryonal carcinoma.
• OCT3/4 -ve.
• Alpha-1-antitrypsin +ve (abbreviated A1A).
• CDX2 +ve in 8 of 20 cases with YST (versus glypican-3).
• SOX2 -ve (0 of 17).
• SOX17 +ve (17 of 17 cases).

Key stains:

• SALL4 +ve, AE1/AE3 +ve, CD30 -ve, glypican-3 +ve.

See also

• Germ cell tumours.
• Genitourinary pathology.