The controversial histologic classification of canine subcutaneous whorling tumours: The path to perivascular wall tumours

Abstract

Subcutaneous spindle cell tumours characterized by whorling growth patterns are common in dogs and are identified as a distinct entity. These tumours were misnamed as hemangiopericytomas (HPCs) because of some minor morphological parallels with their human counterparts. In veterinary medicine, the cell of origin of HPC has been under debate for a long time. Some authors have suggested a perivascular origin while others a perineural one. The evidence of the orientation of the neoplastic cells around the vessels and the expression of contractile proteins supported a perivascular origin while S100 expression and an inconsistent vascular connection supported a perineural origin. Despite the morphological similarities with peripheral nerve sheath tumours in humans, the perineural origin was supported mainly by the expression of markers with low specificity. On the contrary, the majority of studies have supported the perivascular origin of ‘old’ canine HPC. Since a variable degree of myoid‐pericytic differentiation was described, the term perivascular wall tumours (PWTs) were suggested to substitute HPC. Once the diagnostic criteria of PWTs were defined, the clinical behaviour and prognostic variables were investigated, demonstrating differences as compared with the group of canine soft tissue sarcomas (STSs) in general. PWTs are less aggressive, mostly locally invasive, and rarely metastasizing. Their behaviour seems to be less influenced by histological grade, suggesting that canine STSs are heterogeneous. The study of the biological behaviour of specific STS tumour types may be valuable in detecting differences which have passed unnoticed when STSs have been studied concomitantly.

Evaluation of the neoplastic infiltration of the skin overlying canine subcutaneous soft tissue sarcomas: An explorative study

“…Another limitation was that these sSTSs were not subclassified by immunohistochemistry to precisely identify the exact histotype 23,24 . In 23 cases, the sSTSs were classified as PNSTs or PWTs according to their morphology while, for the remaining six, a clear classification was not obtained.…”

Prognostic impact of clinical, haematological, and histopathological variables in 102 canine cutaneous perivascular wall tumours

“…The histopathological diagnosis was based on the presence of spindle to polygonal or stellated cells and vascular growth patterns consistent with PWT (perivascular whorls, staghorn vessels, placentoid, and medial/intimal bundles) 1,2,4 . Immunohistochemistry was added if needed to obtain definitive diagnosis 1 .…”

“…Pulmonary metastases are rarely reported, and rates of local recurrence (LR) are relatively low, with one paper estimating a probability of being free from LR of 98% at 6 months, 92% at 1 year, 80% at 2 years and 76% at 3 years 2 . However, the definition of prognostic factors for PWTs is desirable to identify the subpopulation of dogs at risk for tumour relapse that may benefit from a higher surgical dose or adjuvant treatment 4 . Two previous studies have investigated the prognostic impact of clinical and histological variables on 55 and 56 surgically excised PWTs 2,3 .…”

“…Tumour size and depth have been correlated with a higher hazard of LR, whilst histological grading, which is a well‐established prognostic factor for STSs does not seem to play a role for PWTs 2,3 . To date, however, the majority of prognostic studies have been conducted on the heterogeneous group of STSs, and prognostic information on a large population of PWTs is still lacking 4 …”

Editorial

“…This special issue, from its origin, was intended to be comprised of papers coming from investigative teams worldwide that are working in veterinary and comparative oncology with specific expertise in sarcomas; therefore, basic research scientists, medical and surgical oncologists, radiotherapists, clinical pathologists and pathologists were all invited to submit relevant reviews or original research manuscripts in the areas of basic or clinical research of sarcomas. Included in this issue are reviews aimed at understanding the clinical and pathological course of sarcomas by refining histologic classification and improving or standardizing histologic margin assessment of sarcomas . Original research manuscripts investigating the basic biology of sarcoma cells include studies evaluating the effects of toceranib phosphate in vitro and in vivo and a potential role for adrenergic receptor antagonists in moderating radiosensitivity .…”