Introduction:
Testicular germ cell tumor is the ideal model for the study of a genetic versus stem cell origin of cancer in solid tumors. Teratoma formation often develops in primary and metastatic germ cell tumors and is resistant to all systemic therapy, requiring surgical extirpation. There is controversy surrounding the genesis of germ cell-associated teratoma and the origin of its ability to transform into malignancy. It is unknown whether a mature teratoma dedifferentiates due to genetic mutations that reprogram a progeny cell into a progenitor cell, or teratoma develops from cancer stem cells, enabling it to differentiate into multiple lineages. The hypotheses of differentiation versus dedifferentiation in cancer cannot by more diametrically opposite and conceptually pivotal. We hypothesize that somatic transformation occurs by differentiation of a progenitor stem-like cell embedded in the teratoma rather than by dedifferentiation of a progeny differentiated cell from acquisition of a specific genetic mutation or activation of a specific stem-ness gene.
Methods:
Two investigations where explored to further evaluate this hypothesis: (1) develop a post-chemotherapy teratoma primary culture and demonstrate a stem cell-like progenitor cell embedded within teratoma derived from surgically resected specimens, and (2) evaluate the genetic and molecular profiles of metastatic teratoma and corresponding malignant transformation in surgically resected specimens. After successful develop of a teratoma primary culture, flow cytometry was performed on live cells for cell-surface stem-ness markers to identify a potential cancer stem cell within the teratoma. Subsequent implantation of in vitro primary cultures into SCID mice created in vivo patient derived xenograft (PDX) models. Second, archival tumor tissue from 7 patients with mapped H&E stained slides and unstained sections of the teratoma and its associated somatically transformed tumor was used for DNA and RNA sequencing. Genomic DNA and RNA, library prep, and capture were performed using standard procedures and submitted to the MD Anderson Cancer Center IPCT Lab for whole genome and RNAseq sequencing.
Results:
After screening numerous media, growth factors, and extracellular matrix, teratoma cells were successfully grown in primary culture from two patients, Tera13 and Tera22 (Pic 2). Cells were confirmed as teratoma by final pathology and primary culture analysis for i12p, SALL4, OCT3 and NANOG. By flow cytometry, Tera13 and Tera22, were found to have cells positive for the stem-ness markers CD24, CD26, CD34, CD44, CD90, CD117, Cripto-1, SSEA-1, and SSEA-4. The Tera13 cell line was engrafted into the subcutaneous flank of recipient SCID mice and PDX models revealed teratoma tumor at resection (Pic 1). In the second investigation arm using the T200 panel for DNA analysis, we identified 58 genes harboring mutations in 14 archived tumor samples (7 patients), of which 24 genes indicated discordance between teratoma and somatic transformation. None of the 24 genes were consistently altered between patients, thus, teratoma and transformed tissue had similar genetic profiles. RNA analysis revealed 7 significant genes with increased expression in teratoma tissue compared to somatic transformation, suggesting a different epigenetic profile between tissue types.
Conclusion:
For the first time ever reported, we successfully created primary culture teratoma cell lines and subsequent PDX modeling. In addition, we have begun to identify cancer stem-like cells within mature teratoma, suggesting a new hypothesis for predicting teratoma behavior and somatic transformation. By demonstrating that metastatic teratomas and their corresponding somatic transformations had similar if not identical genetic profiles, we hypothesize they have a common clonal origin and question the theory of acquiring specific genetic mutations, which lead to dedifferentiation of teratomas during somatic transformation. We proposed an alternative hypothesis in which teratoma contains a stem-cell entity that could both differentiate into a teratoma or any other tumor phenotype. These entrenched stem-like progenitor cells embedded within the teratoma would account for the malignant potential of teratomas, the necessary extirpation with curative intent, the ability to differentiate and produce intratumoral heterogeneity (including somatic transformation), the propensity to metastasize and to develop late recurrences.
Funding: N/A
Origin of germ cell tumors: somatic transformation and the presence of cancer stem-like cells in teratoma
Category
Testicular Cancer
Description
Poster # / Podium #1
Young Urologic Oncologists (YUO) Program
12/6/2019
8:00 AM - 8:30 AM
Presented By: Eric Umbreit
Authors:
Eric Umbreit
Shi-Ming Tu
Andrew McIntosh
Mary Beth Westerman
Daniel Shapiro
Aron Joon
Jose Karam
Christopher Wood