Abstract
Editor:
We would like to thank Drs Wright, Pinto-Rojas, Trevenen, and Yu for their interest in our 2007 publication “Three Equine Cases of Mixed Hepatoblastoma With Teratoid Features.” 4 Wright et al voiced concern on the priority and appropriate usage of the term teratoid features in our diagnoses.
First, we are sorry if Wright et al misinterpreted our statement regarding priority of the term, which read, “To the authors' knowledge, these cases are the first to describe mixed hepatoblastomas with teratoid features in an equine fetus (case No. 1) and 2 neonates (cases No. 2 and No. 3).” We did not imply that these cases were the first reports of hepatoblastomas with teratoid features in any species. We merely intended to note the first reports of these tumors in fetal or neonatal horses. As Wright et al noted, the teratoid nomenclature has been in common but inconsistent usage for a number of years.
More important, we would like to defend our diagnoses of mixed hepatoblastomas with teratoid features. Because hepatoblastomas are rare in horses and other domesticated animals, the premise for the nomenclature stemmed from the human literature. Wright et al made an important point that “there is not uniform agreement on the precise criteria to diagnose ‘teratoid.’” Our use of the term stemmed from the book Pathology of the Liver 1 and other citations that describe teratoid features in hepatoblastomas to include stratified squamous epithelium, melanin pigment, mucinous epithelium, embryonic tubules, cartilage, bone, striated muscle, endocrine tissue, or neural tissue. 1,2,6 Other generalists are even less specific; they define teratoid features in hepatoblastomas as “elements typically not seen in developing or adult liver.” 6 Because all 3 of the equine hepatoblastomas in our article contained 1 or more nonindigenous features listed above, we thought it appropriate to apply the term teratoid. Because the diagnosis of a mixed epithelial–mesenchymal hepatoblastoma with nonindigenous cell populations was obvious in all 3 of our cases, we did not request input from human pediatric pathologists. Frankly, it was not until we read the letter by Wright et al that we learned of the inconsistent usage of the term teratoid in the human literature. Based on this inconsistency, we believe that the usage of teratoid features in the hepatoblastoma nomenclature needs to be standardized among pathologists, both medical and veterinary.
We believe that the broad and simple definition of teratoid, based on the presence of nonindigenous cell populations, seems logical and sufficient owing to the likely underlying mechanism associated with the development of these features. Hepatoblastomas contain and probably derive from pluripotent stem cells. 2,3,5 The presence of different teratoid features in hepatoblastomas most likely reflect the differentiation of these stem cells into different nonindigenous cellular lineages.
We acknowledge that these equine hepatoblastomas do not meet the criteria for the purist’s definition of teratoid features; however, all 3 tumors had one or more of the characteristics previously classified as teratoid features in the literature. Although the tumors did not differentiate into diverse cellular lineages, they did differentiate into cellular populations that are nonindigenous to the liver. It is the presence of these nonindigenous lineages in combination with the cited literature that we justify our diagnoses of mixed hepatoblastomas with teratoid features.
Although we do not retract our diagnoses, we do acknowledge that some purists would not consider the features identified in those tumors as being sufficient for subclassification as mixed epithelial–mesenchymal hepatoblastomas with teratoid features. We believe that the debate on the definition of teratoid features in hepatoblastomas should focus on the inconsistencies in the literature. Regardless of the appropriateness of the term teratoid, these 3 cases were the first reported mixed epithelial–mesenchymal hepatoblastomas with nonindigenous cell differentiation in fetal and neonatal horses.
We thank Drs Wright, Pinto-Rojas, Trevenen, and Yu for bringing the inconsistencies in the nomenclature of hepatoblastomas to light. We are additionally pleased to see our medical pathology colleagues take interest and offer opinions in the field of veterinary and comparative pathology.