The use of alkaline phosphatase and runx2 to distinguish osteosarcoma from other common malignant primary bone tumors in dogs

Immunohistochemical Characterization of Feline Giant Cell Tumor of Bone (GCTb): What We Know and What We Can Learn from the Human Counterpart

Giant cell tumor of bone (GCTb), formerly also known as osteoclastoma, is a pathological entity that in veterinary medicine is still undefined and, probably, underdiagnosed. In humans, GCTb is recognized as a primary benign bone tumor, locally aggressive, with high local recurrence rates, with controversial histogenesis that can rarely progress or present as a malignant form. In pets, this tumor is still considered rare, though the possibility of underdiagnosis is significant. Hence, the aim of the present study is to provide a histological and immunohistochemical characterization of a small case series of presumptive feline GCTb, comparing our results to the data reported for the human counterpart. Searching our archive, we found, from 2010 to 2023, only three diagnosed cases of GCTb from domestic cats (felis catus). After diagnosis revision, the samples were submitted to immunohistochemistry for Iba1, TRAP, SATB2, RUNX2, RANK, karyopherin α2 (KPNA-2), and osteocalcin. Ki-67 index was also evaluated. Results showed that the multinucleated giant cells were positive for Iba1, TRAP, and RANK, accounting for their osteoclastic origin. On the other side, mononuclear cells were mostly positive for osteoblast markers such as RUNX2, SATB2, and KPNA-2, whereas tumor-associated macrophages showed positivity for Iba1. Hence, results on the cell types characterizing the feline GCTb were comparable to those described in the human form of the tumor. Currently, diagnostic criteria for GCTBs in cats and, in domestic animals more broadly, are still lacking. This study provides valuable data into the immunohistochemical characteristics of the cell populations in feline GCTBs, enhancing veterinarians' and pathologists' knowledge for its diagnosis, ultimately improving patient care. Larger case series, complete with follow-up information, molecular analyses for specific mutations, and imaging of both tumors and patients, are needed to improve identification and achieve greater sensitivity in diagnosing this unique tumor.

Expression of osteogenic proteins in kidneys of cats with nephrocalcinosis

BACKGROUND

Nephrocalcinosis is a common pathological finding in cats with chronic kidney disease and nephrolithiasis. Understanding its pathogenesis may identify future therapeutic targets.

HYPOTHESIS

Nephrocalcinosis is associated with expression of an osteogenic phenotype.

ANIMALS

Kidneys with medullary mineralization were obtained from 18 cats (10 with and 8 without nephroliths) undergoing necropsy.

METHODS

Cross-sectional study. Microradiography and histopathology (modified von Kossa stain) were used to confirm parenchymal mineralization. Immunohistochemistry for 5 osteogenic markers was performed to determine their co-localization with nephrocalcinosis. The proportion of kidneys with stronger immunointensity in mineralized versus non-mineralized regions was analyzed using 1-tailed sign tests. The proportion of kidneys with co-localization of nephrocalcinosis and each marker was compared between kidneys with and without nephroliths using Fisher's exact tests.

RESULTS

Nephrocalcinosis co-localized with osteopontin immunoreactivity in all 18 cats (100%) and with osteocalcin in 12 cats (67%). Both osteogenic markers had stronger immunointensity in mineralized regions compared with non-mineralized regions. Limited co-localization was observed with other markers: bone morphogenic protein-2 in 2 kidneys (both with nephroliths) and tissue non-specific alkaline phosphatase in 1 kidney (without nephroliths); runt-related transcription factor-2 was undetected. No statistically significant differences were found in the co-localization of nephrocalcinosis with osteogenic proteins between kidneys with and without nephroliths.

CONCLUSIONS AND CLINICAL IMPORTANCE

Expression of osteogenic proteins in areas of nephrocalcinosis indicates that nephrocalcinosis is associated with the development of an osteogenic phenotype. Targeting these processes could offer a novel approach to prevent nephrolithiasis at its origin.

Special AT-rich sequence-binding protein 2 immunohistochemistry in the diagnosis of osteosarcoma in dogs

Malignant osteoblasts can have markedly pleomorphic phenotypes and variable amounts of tumour-associated matrix, complicating the ability of pathologists to accurately differentiate osteosarcoma (OSA) from other types of neoplasms using only histopathology. Current immunohistochemical markers for animals have limited sensitivity and specificity in identifying OSA or produce inconsistent results. Immunohistochemistry (IHC) for special AT-rich sequence-binding protein 2 (SATB2) has been used in human medicine to aid in identification of normal and neoplastic osteoblasts, and the objective of this study was to determine whether this marker could also be useful for the diagnosis of canine OSA. Initially, SATB2 IHC was performed on eight samples from cases of well-differentiated canine OSA and on other tumour types for which OSA is a differential diagnosis, as well as on normal tissues, to assess sensitivity and cross-reactivity. Following confirmation that SATB2 is immunoreactive for normal and neoplastic canine osteoblasts and negative in other non-osseous mesenchymal cell types and organs, SATB2 IHC was tested on 123 cases of poorly differentiated malignant neoplasms as part of a panel with other immunohistochemical markers, as appropriate, based on histomorphology and differential diagnoses. The conclusion is that SATB2 IHC is a sensitive and specific marker for identifying canine OSA when used in a panel with other immunohistochemical markers and in conjunction with supportive clinical history.

Metastatic Osteosarcoma of the Distal Femur in a Korean Water Deer (Hydropotes inermis argyropus)

A free-living female Korean water deer (Hydropotes inermis argyropus) was found with swelling in the left femur. Radiographic and histopathologic examination confirmed distal femoral osteosarcoma with metastases to the inguinal lymph node and the lungs; there are no previous reports of osteosarcoma in water deer.

Effects of Erythropoietin-Promoted Fracture Healing on Bone Turnover Markers in Cats

In orthopaedics, erythropoietin (EPO) is applied in the preoperative management of anaemic patients, but also as a stimulating factor to assist bone regeneration due to its angiogenic and osteoinductive potential. Since orthopaedists mainly rely on their clinical experience to assess bone healing, additional and more objective methods such as studying the dynamics of bone markers are needed. Therefore, the aim of this study was to investigate the plasma activity of bone-specific alkaline phosphatase (BALP), the N-terminal propeptide of type I collagen (PINP), the C-terminal telopeptide of type I collagen (CTX), and deoxypyridinoline (DPD) during the first 2 months of healing of comminuted fractures in cats, either non-stimulated or locally stimulated with recombinant human erythropoietin (rhEPO). The study included twelve cats of mixed breeds, aged 7.2 ± 4 months, weighing 2.11 ± 1.1 kg, with comminuted diaphyseal fractures of the femur. Surgical treatment with plate osteosynthesis was performed in all animals. The cats were randomly divided into two groups-a control (n = 6) and an EPO group (n = 6). The locally applied EPO leads to the increased activity of bone formation markers (BALP and PINP) during the second week after the osteosynthesis, preceding the peaks in the control group by two weeks. The studied bone resorption markers (DPD, CTX) varied insignificantly during the studied period. In conclusion, erythropoietin could serve as a promoter of bone healing in comminuted fractures in cats.

Telangiectatic osteosarcoma in four dogs: Cytologic, histopathologic, cytochemical, and immunohistochemical findings

Telangiectatic osteosarcoma is a rare variant of osteosarcoma histologically and clinically similar to hemangiosarcoma (HSA). This case series describes the imaging and cytologic features of four histologically confirmed telangiectatic osteosarcomas, including the use of cytochemical stains. Alkaline phosphatase (ALP) was applied to Wright-Giemsa-stained cytology slides, and Factor VIII immunohistochemistry was evaluated. Cytologic characteristics included atypical mesenchymal cells with evidence of acute and chronic hemorrhage. Telangiectatic osteosarcoma cases had positive ALP cytochemical staining, while control HSA cases were negative. Factor VIII immunohistochemistry was negative in telangiectatic osteosarcoma and positive in HSA. Cytologic diagnosis of telangiectatic osteosarcoma with positive ALP cytochemical staining can help differentiate this neoplasm from HSA.

Canine soft tissue sarcomas: the expression of RUNX2 and karyopherin alpha-2 in extraskeletal (soft tissues) and skeletal osteosarcomas

Extraskeletal osteosarcoma (EOS) is a malignant tumor producing bone matrix and/or chondroid material, without direct attachment to bone or periosteum. In humans and dogs, EOS is highly infiltrating, rapidly growing, often characterized by osteoid deposition and variable ossification, similar to primary skeletal osteosarcoma (SOS). In dogs, EOS arises from visceral and soft tissue locations, occasionally in trauma or foreign body sites, or in granulomas. Few data are currently available on the phenotype of these tumors. The present study aims to assess the expression RUNX2 and Karyopherin alpha-2 in EOS, comparing it with SOS and the data available from the human counterpart. Seventeen cases of canine osteosarcoma (13 EOS and 4 SOS) were retrospectively selected and submitted to immunohistochemistry for RUNX2 and Karyopherin alpha-2. Our results showed that, in EOS, RUNX2 is expressed in a mean of 73.07 ± 5.36 neoplastic cell nuclei, in face of a mean 36.15 ± 6.25 of Karyopherin alpha-2 positive nuclei. Osteoclasts, when present, were negative for both markers. No correlation was observed among the two markers (p > 0.05), nor statistically significant difference in quantitative expression was assessed comparing EOS and SOS groups. RUNX2 is expressed in canine EOS similarly to SOS and could be used as a diagnostic marker in a larger panel. Karyopherin alpha-2 is expressed in canine EOS and SOS similarly to human SOS and could be validated in future studies as an additional diagnostic marker. Further studies should be planned to evaluate the expression of these proteins as prognostic predictive parameters.