Metronomic therapy with cyclophosphamide and piroxicam effectively delays tumor recurrence in dogs with incompletely resected soft tissue sarcomas

Background: Continuous administration of low doses of cyclophosphamide and standard doses of cyclooxygenase‐inhibiting drugs has been shown to suppress tumor angiogenesis, reverse immunosuppression, and deplete regulatory T cells in cancer models. Hypothesis: We hypothesized that continuous treatment with low‐dose cyclophosphamide and full‐dose piroxicam would delay tumor recurrence in dogs with soft tissue sarcomas (STS). Animals: Eighty‐five dogs with incompletely resected STS, 30 treated dogs, and 55 contemporary control dogs. Methods: Treatment outcomes in 85 dogs with incompletely resected STS were evaluated in a retrospective study. Dogs in the treatment group received continuously administered low‐dose cyclophosphamide (10 mg/m²) and standard dose piroxicam (0.3 mg/kg) therapy. Time to local tumor recurrence (disease‐free interval; DFI) was compared between the 30 treated dogs and 55 untreated control dogs matched for age and tumor site and grade. Results: DFI was significantly (P < .0001) prolonged for STS of all sites (trunk and extremity) in treated dogs compared with untreated control dogs. The DFI also was significantly longer in treated dogs when tumor site (trunk and extremity) was compared. Twelve treated dogs (40%) experienced mild toxicity (grade 1 and 2) at some point during treatment and 1 dog developed grade 4 cystitis. Every other day dosing was tolerated better than daily dosing. Conclusions: Metronomic therapy with cyclophosphamide and piroxicam was very effective in preventing tumor recurrence in dogs with incompletely resected STS. These findings suggest that further evaluation of this approach is warranted as adjuvant therapy in dogs with highly metastatic tumors such as osteosarcoma and melanoma.     

Low-dose cyclophosphamide selectively decreases regulatory T cells and inhibits angiogenesis in dogs with soft tissue sarcoma

Background: Low‐dose, continuous (metronomic) chemotherapy improves tumor control by inhibiting tumor angiogenesis and suppressing regulatory T cells (Treg) in mice and humans. The effects of metronomic chemotherapy on Treg and tumor angiogenesis in dogs has not been investigated previously. Objective: To determine whether metronomic cyclophosphamide (CYC) therapy decreases Treg or exhibits antiangiogenic activity or both in dogs with soft tissue sarcoma (STS). We hypothesized that Treg numbers would be increased in dogs with STS and that continuous dosing of CYC would decrease Treg in a dose‐dependent manner, as well as exhibit antiangiogenic activity. Animals: Eleven client‐owned dogs with grade I or II STS. Twenty‐one healthy dogs were used as controls. Methods: Prospective, open, clinical trial. Dogs with STS were enrolled in 2 dose cohorts and administered CYC at 12.5 or 15 mg/m² PO once daily for 28 days. Whole blood and tumor biopsy specimens were obtained on days 0, 14, and 28 to assess changes in T lymphocyte subsets by flow cytometry and tumor microvessel density (MVD), respectively. Results: Administration of CYC at 12.5 mg/m²/d significantly decreased the number of Treg from days 0 to 28, but there was no change in the percentage of Treg or tumor MVD. In dogs that received CYC at 15.0 mg/m²/d, both the number and percent of Treg as well as tumor MVD were significantly decreased over 28 days. Conclusions: CYC administered at 15 mg/m²/d should be used in further studies examining the antitumor properties of low‐dose CYC in dogs.     

Establishment and characterization of a canine soft tissue sarcoma patient‐derived xenograft model

Spontaneously occurring soft tissue sarcoma (STS) is relatively common in canine cancer patients. Because of the similarities to human disease, canine STSs are a valuable and readily available resource for the study of new therapeutics. In this study, a canine patient‐derived xenograft (PDX) model, CDX‐STS2, was established. The CDX‐STS2 model was engrafted and expanded for systemic administration studies with chemotherapeutic agents commonly used to treat STS, including doxorubicin, docetaxel and gemcitabine. Immunohistochemistry for drug‐specific biomarkers and tumour growth measurement revealed tumour sensitivity to doxorubicin and docetaxel, whereas gemcitabine had no effect on tumour growth. Although many human PDX tumour models have been established, relatively few canine PDX models have been reported to date. CDX‐STS2 represents a new STS PDX research model of canine origin that will be useful in bridging preclinical research with clinical studies of STS in pet dogs.     

PD‐1 expression by canine T cells and functional effects of PD‐1 blockade

The co‐inhibitory checkpoint molecule programmed death receptor 1 (PD‐1) can trigger T cell functional exhaustion upon binding to its ligand PD‐L1 expressed on tumour cells or macrophages. PD‐1 blocking antibodies have generated remarkable results in human cancer patients, including inducing durable responses in a number of advanced cancers. Therefore, monoclonal antibodies specific for canine PD‐1 were assessed for T cell binding and induction of functional activation. A total of 5–10% of CD4 T cells and 20–25% of CD8 T cells from healthy dogs expressed PD‐1, and PD‐1 expression was upregulated on T cells from dogs with cancer. Functionally, PD‐1 antibodies significantly enhanced T‐cell activation, as assessed by proliferation and interferon‐gamma (IFN‐γ) production. PD‐1 antibodies also reversed T‐cell suppression induced by canine soluble PD‐L1 and by tumour cells and tumour explant fragments. These findings indicate that PD‐1 antibodies have potential for use in cancer immunotherapy in dogs.     

Calcitriol (1,25‐dihydroxycholecalciferol) enhances mast cell tumour chemotherapy and receptor tyrosine kinase inhibitor activity in vitro and has single‐agent activity against spontaneously occurring canine mast cell tumours*

Calcitriol potentiates the effect of multiple chemotherapy agents in a variety of tumour models. In this study, we examine whether calcitriol increases chemotherapy or tyrosine kinase inhibitor in vitro cytotoxicity in canine mastocytoma C2 cells. We also evaluate the in vivo effect of DN101, a highly concentrated oral formulation of calcitriol designed specifically for cancer therapy, as a single‐agent therapy in dogs with mast cell tumours (MCTs). Calcitriol exhibits synergistic, antiproliferative activity when used in combination with CCNU, vinblastine, imatinib or toceranib in vitro. The concentrations required for 50% growth inhibition were generally two‐ to six‐fold lower when the drugs were used in combination than when used individually. High‐dose oral calcitriol induced remission in 4 of 10 dogs (one complete remission, three partial remissions), although the majority experienced toxicity, necessitating discontinuation of the trial. Further evaluation of calcitriol in combination therapy for dogs with MCTs is warranted.     

Association of cerebrospinal fluid analysis findings with clinical signs and outcome in acute nonambulatory thoracolumbar disc disease in dogs

Background: Cerebrospinal fluid (CSF) pleocytosis recently was associated with the severity of neurologic signs in dogs with intervertebral disc disease (IVDD). Hypothesis/Objectives: To look for an association among CSF cell counts, total protein concentration, and severity of neurologic signs at presentation with outcome in dogs with acute thoracolumbar IVDD. Our hypothesis was that CSF total nucleated cell count (TNCC) and percentage cell types would be associated with the severity of spinal cord damage and therefore with both the presenting clinical signs and the prognosis of affected dogs. Animals: Fifty‐four dogs with acute nonambulatory thoracolumbar IVDD were evaluated. Methods: Retrospective study. Signalment, neurologic grade, CSF TNCC, protein concentration, red blood cells count and differential cell percentages, and short‐ and long‐term outcomes were evaluated. Results: CSF pleocytosis (>5 cells/μL) was present in 54% of dogs and was positively associated with neurologic grade at presentation and with postoperative time to regaining ambulation. Neutrophils were observed most frequently. The percentage of CSF macrophages and macrophage to monocyte ratio were higher (P= .001, for both) in dogs presented without deep pain sensation (DPS) that did not regain ambulation. Receiver operator characteristics curve analysis yielded a cut‐off point of 13% macrophages with a sensitivity and specificity of 100 and 83%, respectively, for prediction of a negative outcome. Conclusions and Clinical Importance: CSF pleocytosis is positively associated with the severity of spinal cord damage in dogs with thoracolumbar IVDD. The percentage of CSF macrophages can be used as a prognostic indicator for regaining ambulation in dogs that have lost DPS.     

Identification of novel tumour‐associated antigens in canine mammary gland tumour

Canine mammary gland tumour (MGT) is the most common neoplasm in female dogs and has similar biological characteristics to human MGT. Spontaneous canine MGT is a more attractive clinical model in oncological research than that of the murine experimental model. Tumour‐associated antigens (TAAs), which are produced in tumour cells, are applied as tumour markers, tumour vaccine antigens and molecular targets of therapeutic drugs. In this study, we have primarily identified 13 different TAAs of canine MGT by serological immunoscreening of cDNA expression library. The results of serological mini‐arrays of identified antigens showed that CCDC41 antigen specially reacted with 35% of sera from MGT‐dogs and did not react with control sera. We also found that HSPH1 mRNA expression levels increased significantly in MGT tissues. These findings will contribute to the development of diagnostic technologies and translational target therapies for dogs. Clinical relevance : HSPH1, which is strongly expressed in the tumour tissue, will be a possible vaccine antigen of canine MGT.     

Detection of synovial macrophages in the joint capsule of dogs with naturally occurring rupture of the cranial cruciate ligament

OBJECTIVE: To test the hypotheses that the densities of macrophages in the synovial membranes and capsules of stifle joints in dogs with ruptured cranial cruciate ligaments are greater than those of normal joints and that those densities in affected joints are positively correlated with the chronicity and severity of the disease. ANIMALS: 17 dogs with naturally occurring rupture of the cranial cruciate ligament and 5 healthy control dogs. PROCEDURE: All dogs underwent orthopedic and radiographic evaluations. In affected dogs, duration of clinical signs was used as an indicator of disease chronicity and the severity of osteoarthritis in the stifle joint was determined radiographically. Joint capsule specimens were evaluated histologically; macrophages, interleukin-6, and tumor necrosis factor-alpha were identified by use of immunocytochemical techniques. RESULTS: Compared with unaffected joints, macrophage density was increased in all affected joints. Duration of disease was significantly associated with radiographic severity of osteoarthritis and synovial macrophage density. Synovial macrophage density was significantly associated with severity of osteoarthritis and with the presence of interleukin-6 and tumor necrosis factor-a. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that synovial macrophages may be involved in the development of pathologic changes (including osteophyte formation) in the stifle joints of dogs with osteoarthritis secondary to rupture of the cranial cruciate ligament. Determination of the importance of synovial macrophages in the development of changes in osteoarthritic joints may result in new treatment strategies that involve elimination of the deleterious effects of those cells.     

Diagnostic accuracy of pre‐treatment biopsy for grading soft tissue sarcomas in dogs

Histologic grade is an important prognostic factor for both local recurrence and metastatic potential with canine soft tissue sarcoma (STS). Pre‐treatment biopsy with identification of tumour grade may aid in prognostication and determination of surgical margins necessary for local control. The purpose of this study was to evaluate the grading accuracy of various pre‐treatment biopsy techniques (wedge, punch, needle‐core) for STS in dogs. Medical records of 68 dogs diagnosed with a STS via pre‐treatment biopsy and confirmed by excisional biopsy were evaluated. The concordance in grade between excisional and pre‐treatment biopsies was 59%. Of the 41% that lacked concordance, 29% of pre‐treatment biopsies underestimated and 12% overestimated grade. The method of pre‐treatment biopsy did not significantly effect grade concordance. Based on these data, needle‐core biopsy appears to be similar in accuracy compared to open biopsy, however, grading determined by pre‐treatment biopsy in general should be interpreted with caution.     

Cancer stem cell populations in lymphoma in dogs and impact of cytotoxic chemotherapy

Cancer relapse following chemotherapy has been attributed in part to the presence of cancer stem cells (CSC), which drive tumour growth and metastasis and are highly resistant to the effects of cytotoxic chemotherapy. As a result, treatment with cytotoxic chemotherapy selects for drug‐resistant CSC populations that eventually drive tumour recurrence. Little is known currently regarding the role of CSC in dogs with lymphoma, nor the impact of chemotherapy on CSC populations. Therefore, we prospectively quantitated CSC populations in dogs with B‐cell (BCL) and T‐cell lymphoma (TCL), using tumour aspirates and flow cytometric analysis with a panel of CSC markers. In addition, in vitro studies were carried out to determine the impact of chemotherapy resistance on the stem cell phenotype and stem cell properties of lymphoma cells. We found that the percentages of tumour cells expressing CSC markers were significantly increased in dogs with BCL, compared with B cells from normal lymph nodes. Similar findings were observed in dogs with TCL. In vitro studies revealed that lymphoma cells selected for resistance to CHOP chemotherapy had significantly upregulated expression of CSC markers, formed spheroids in culture more readily, and expressed significantly greater aldehyde dehydrogenase activity compared with chemotherapy‐sensitive tumour cells. Similar results were observed in tumour samples dogs with relapsed BCL. These findings suggest that cytotoxic chemotherapy can lead to a relative enrichment of tumour cells with CSC properties, which may be associated with lymphoma recurrence.     

Preclinical evaluation of 5-aminolevulinic acid-based photodynamic therapy for canine transitional cell carcinoma

As a prelude to photodynamic therapy, 5‐aminolevulinic acid (ALA) was given orally to healthy dogs. ALA‐induced protoporphyrin IX (PpIX) fluorescence significantly increased in the mucosa of the urinary bladder in an ALA dose‐dependent fashion. Vomiting occurred after ALA administration in 70% of the dogs but did not affect PpIX fluorescence. ALA‐based photodynamic therapy (PDT) of the urinary bladder in healthy dogs caused only submucosal oedema within the bladder wall. No haematologic or serum biochemistry abnormalities were observed after ALA administration. Microscopic haematuria was observed in all the dogs after PDT but was mild and self limiting. ALA‐based PDT was administered to six dogs with transitional cell carcinoma (TCC) of the lower urinary tract. ALA‐based PDT resulted in tumour progression‐free intervals from 4 to 34 weeks in five dogs; one dog with pre‐existing hydronephrosis died shortly after PDT. Dogs with TCC represent an outbred, spontaneous, tumour model for developing PDT protocols for humans with bladder cancer.     

Evaluation of immunomodulatory effect of recombinant human granulocyte‐macrophage colony‐stimulating factor on polymorphonuclear cell from dogs with cancer in vitro

The objective of this in vitro study was to evaluate the immunomodulatory effects of recombinant human granulocyte‐macrophage colony‐stimulating factor (rhGM‐CSF) on polymorphonuclear cell (PMN) function in dogs with cancer. PMNs were harvested from dogs with naturally developing cancer as a pre‐clinical model to evaluate the immunomodulatory effects of rhGM‐CSF on PMN phagocytic and cytotoxic functions, cytokine production and receptor expression. Some aspects of cancer‐related PMN dysfunction in dogs with cancer were restored following incubation with rhGM‐CSF including PMN phagocytosis, respiratory burst and LPS‐induced TNF‐α production. In addition, rhGM‐CSF increased surface HLA‐DR expression on the PMNs of dogs with cancer. These data suggests that dysfunction of innate immune response in dogs with cancer may be improved by rhGM‐CSF. The results of this study provided a pathophysiologic rationale for the initiation of clinical trials to continue evaluating rhGM‐CSF as an immunomodulatory therapy in dogs with cancer.     

Decreased Ratio of CD8+ T Cells to Regulatory T Cells Associated with Decreased Survival in Dogs with Osteosarcoma

Background: Increased numbers of regulatory T cells (Treg) and decreased ratios of CD8+ T cells to Treg have been shown to correlate with decreased survival times (ST) in humans with certain malignancies. A possible connection between Treg and ST in dogs with cancer has not been investigated previously. Hypothesis: The purpose of this study was to compare numbers of Treg and T lymphocyte subsets in dogs with osteosarcoma (OSA) to those of healthy dogs and to determine whether pretreatment values were associated with disease‐free interval or with ST. We hypothesized that Treg numbers would be increased in dogs with cancer and that dogs with a high percentage of Treg would have a poorer prognosis. Animals: Twelve client‐owned dogs with appendicular OSA were entered into a prospective clinical trial. Twenty‐two healthy dogs were used as controls. Methods: The percentages and numbers of Treg and CD4+ and CD8+ T cells in blood, lymph nodes, and tumors were determined with flow cytometry and compared between dogs with OSA and control dogs. Results: Dogs with OSA had significantly fewer circulating CD8+ T cells and significantly more Treg compared with healthy dogs. The CD8/Treg ratio also was significantly lower in dogs with OSA compared with control dogs. In dogs with OSA, a decreased CD8/Treg ratio was associated with significantly shorter STs. Conclusions: These data support a role for Treg in the immune control of canine OSA and suggest that determination of the CD8/Treg ratio may be useful for assessing outcomes.     

Immune dysregulation and osteosarcoma: Staphylococcus aureus downregulates TGF‐β and heightens the inflammatory signature in human and canine macrophages suppressed by osteosarcoma

Since William Coley utilized bacterial immunotherapy to treat sarcomas in the late 19th century, an association between infection and improved survival has been reported for human and canine osteosarcoma patients. One of the reasons for this improved survival is likely a reactivation of the host immune system towards an inflammatory anti‐tumour response, and one of the key players is the macrophage. Yet, despite their importance, the response of macrophages to infectious agents in the context of osteosarcoma has not been thoroughly evaluated. The aim of this study was to evaluate how in vitro exposure to a bacterial agent (Staphylococcus aureus) influenced canine and human macrophage differentiation in the presence of osteosarcoma. Our hypothesis was that S. aureus would, in the presence of osteosarcoma, induce a macrophage phenotype with significantly increased inflammatory signatures. Consistent with our hypothesis, human macrophages co‐cultured with osteosarcoma and S. aureus exhibited increased IFN‐γ, TNF‐α and IL‐12p70 cytokine secretion, decreased TGF‐β cytokine secretion and increased mRNA expression of TNF‐α when compared with macrophages co‐cultured with osteosarcoma and to macrophages cultured alone. Canine macrophages similarly exhibited increased IFN‐γ and TNF‐α cytokine secretion, decreased TGF‐β cytokine secretion, increased mRNA expression of TNF‐α and increased surface receptor expression of CD80 when co‐cultured with osteosarcoma and S. aureus. Collectively, the findings of this study suggest that infection upregulates the inflammatory immune response to counteract osteosarcoma‐induced immune suppression. This work informs a potential therapeutic strategy to optimize inflammatory stimuli for triggering an anti‐osteosarcoma macrophage response.     

Pituitary–adrenal axis function in dogs with neoplasia*

Adrenocorticotropic hormone (ACTH) stimulation tests were done in healthy and tumour‐bearing dogs. In the tumour‐bearing dogs, plasma endogenous ACTH (eACTH) concentration was measured and adrenal gland size was assessed ultrasonographically. Measurements in the tumour‐bearing dogs were taken prior to therapy. No difference existed in basal or ACTH‐stimulated cortisol concentration between tumour‐bearing and healthy dogs. No difference existed in eACTH concentration between dogs with non‐haematopoietic neoplasia (NHN) and lymphoma. However, of 20 dogs with lymphoma, 15% had increased basal serum cortisol concentration, 5% had an exaggerated response to ACTH and 5% had an increased eACTH concentration. Of 15 dogs with NHN, 20% had increased basal cortisol concentration, 7% had an exaggerated ACTH response and no dogs had an increased eACTH concentration. Of the dogs with lymphoma and NHN, 5 and 13%, respectively, had decreased basal cortisol concentrations; 20% of dogs with lymphoma and 13% with NHN had a subnormal ACTH response. eACTH levels were below the reference range in 10% of dogs with lymphoma and 7% with NHN. Overall, 10 adrenal glands were enlarged in seven dogs, five with lymphoma and two with NHN. The clinical significance of these findings remains to be determined.     

Circulating let‐7g is down‐regulated in Bernese Mountain dogs with disseminated histiocytic sarcoma and carcinomas – a prospective study

Cancer is a prevalent cause of mortality in Bernese mountain dogs (BMDs). Circulating microRNAs (miRNAs) are found in blood and have been identified as promising biomarkers in various neoplastic diseases in humans. In the current study, the expression profile of different types of miRNAs was investigated in healthy BMDs and BMDs with cancer. Seven healthy and six non‐treated BMDs with cancer [four with disseminated histiocytic sarcomas (DHS)] were enrolled in this study. Clinical evaluations including physical examination, blood analysis, urinalysis and diagnostic imaging were performed on all dogs. Twenty‐four different miRNAs were profiled from RNA isolated from whole blood preserved in PAXgene^® tubes using quantitative real‐time PCR (qPCR). The miRNA let‐7g was significantly down‐regulated in dogs with cancer (P = 0.002) and dogs with DHS (P = 0.011) compared with healthy controls. This miRNA is a known tumour suppressor and further analyses are warranted to assess its value as a non‐invasive biomarker for early detection of different types of cancer in BMDs.     

Role of monocyte recruitment in hemangiosarcoma metastasis in dogs

Canine hemangiosarcoma (HSA) is a highly malignant tumour associated with short survival times because of early and widespread metastasis. In humans and rodents, monocytes play key roles in promoting tumour metastasis through stimulating tumour cell extravasation, seeding, growth and angiogenesis. Therefore, we investigated the potential association between monocyte infiltration and tumour metastasis in HSA and other common canine tumours. Immunohistochemistry was used to quantify CD18⁺ monocytes within metastases. We found that HSA metastases had significantly greater numbers of CD18⁺ monocytes compared with metastases from other tumour types. HSA cells were the highest producers of the monocyte chemokine CCL2, and stimulated canine monocyte migration in a CCL2 dependent manner. These results are consistent with the hypothesis that overexpression of CCL2 and recruitment of large numbers of monocytes may explain in part the aggressive metastatic nature of canine HSA. Thus, therapies designed to block monocyte recruitment may be an effective adjuvant strategy for suppressing HSA metastasis in dogs.     

Retrospective evaluation of blood copper stable isotopes ratio 65Cu/63Cu as a biomarker of cancer in dogs

Previous studies in humans with breast, colorectal or liver cancer showed that neoplasia was associated with a modification of the blood ratio between ⁶⁵Cu and ⁶³Cu (?Cu). The aim of the present study was to compare the blood ?Cu of dogs with cancer to healthy controls or dogs with non‐oncologic disease. One hundred and seventeen dogs were included in the study (35 dogs with cancer, 33 dogs with non‐neoplastic disease, and 49 healthy controls). The ?Cu of dogs with cancer was significantly lower than the ratio of healthy controls (P < 0.0001) but not significantly different from dogs with non‐oncologic disease. Six dogs with lymphoma were also evaluated after they achieved clinical remission and five out of six had an increase of ?Cu. Further studies are warranted but these results suggest that ?Cu could help in the diagnosis of cancer in a controlled clinical context, and may be a potential biomarker for the follow‐up of cancer.     

Quantification of plasma DNA as a prognostic indicator in canine lymphoid neoplasia

Dogs have a similar incidence of spontaneous cancers as people, and a noninvasive test to monitor disease status in dogs would be of great value. Humans with cancer often have increased levels of cell‐free circulating DNA in their plasma, which has shown promise for diagnosis, prognosis and detection of residual disease. We hypothesized that dogs with cancer have increased circulating DNA compared with healthy dogs or dogs with non‐neoplastic diseases. Plasma DNA was measured in 40 healthy dogs, 20 dogs with non‐neoplastic diseases and 80 dogs with cancer. The reference interval for plasma DNA in healthy dogs was 1–15 ng mL^?1. Dogs with lymphoma and lymphoid leukaemia had significantly higher concentrations (range: 0–91 ng mL^?1, P < 0.0001). Antigen receptor rearrangement assays suggest that plasma DNA had the same clonality as the primary lymphoid tumours. Dogs with lymphoid neoplasia and plasma DNA >25 ng mL^?1 had shorter remission times than those with < 25 ng mL^?1 (P= 0.0116). In contrast to humans, where increased plasma DNA is seen in many diseases, dogs with nonlymphoid malignancies and non‐neoplastic diseases had plasma DNA concentrations similar to healthy dogs. This study shows that a portion of dogs with lymphoid neoplasia have increased tumour‐derived plasma DNA, which serves as a negative prognostic indicator.     

Evaluation of cyclooxygenase-1 and cyclooxygenase-2 expression and the effect of cyclooxygenase inhibitors in canine prostatic carcinoma

Prostatic carcinoma occurs primarily in older castrated male dogs and is typically a fatal disease (most dogs die within few months after the initial diagnosis). Surgery, i.e., total prostatectomy, or radiation therapy is often not pursued due to risks of complications and a high rate of distant metastasis. Cyclooxygenase‐2 (Cox‐2) expression has been documented in several malignancies, including canine prostatic carcinoma. Cox‐2 inhibition has been reported to have preventative effects on several human malignancies and has therapeutic effects on both laboratory and spontaneous tumour models. The purpose of this retrospective study was to evaluate Cox expression and the effects of Cox inhibitors on survival in dogs with prostatic carcinoma. 94.1 and 88.2% of the tumours expressed Cox‐1 and Cox‐2, respectively. Furthermore, dogs treated with Cox inhibitors (piroxicam or carprofen) lived significantly longer than untreated dogs, 6.9 versus 0.7 months (P < 0.0001), suggesting that Cox inhibitors may have an important role in canine prostate cancer therapy.