Metastatic Germ Cell Tumors Often Represent Continuous Evolving Processes (Somatic Transformation) toward SALL4-Positive Dominant Yolk Sac Tumors and Teratomas

Abstract Introduction/Objective SALL4 has been used to diagnose primary and metastatic germ cell tumors (GCT). However, it is not well established if SALL4 represents an evolving biomarker for GCT during the metastatic processes. Methods/Case Report We studied the fetal expression of SALL4 and a small series of metastatic GCT by comparing SALL4 expression (in all levels of GCT) with OCT3/4 expression (mainly in the early chain of germ cell tumors such as seminoma and embryonal carcinoma). Results (if a Case Study enter NA) First, we found SALL4 expression in Wolffian ducts and their surrounding stromal cells of 4 early embryos (5-7 weeks of gestation), implying that SALL4 may be involved in the early genital structure development. Then we identified 6 cases with metastatic GCT and compared SALL4 with OCT3/4 stains. The original tumors were all positive for both OCT3/4 and SALL4, but 4 out of 6 subsequently metastatic GCT stained positive only for SALL4 but not for OCT3/4. Particularly in case 5, the first two biopsies for metastatic GCT were positive for both biomarkers, but the last metastatic GCT to the gallbladders was positive only for SALL4. Conclusion Our pilot study raises the possibility that metastatic GCT may represent some evolving process to epithelial differentiated neoplasms (via somatic transformation) namely yolk sac tumor and teratoma along the germ cell differentiation chain. Therefore, SALL4 staining becomes a necessary step to avoid the pitfall of misdiagnosing unusual metastatic tumors with a known and unknown history of GCT particularly in male patients.