Evaluation of intracranial meningioma resection with a surgical aspirator in dogs: 17 cases (1996-2004)

OBJECTIVE: To determine results of intracranial meningioma resection by use of a surgical aspirator and assess prognostic factors associated with intracranial meningiomas in dogs. DESIGN: Retrospective case series. ANIMALS: 17 dogs. PROCEDURES: Medical records of dogs that underwent resection of an intracranial meningioma by use of a surgical aspirator were reviewed. Information pertaining to signalment, imaging findings, clinical signs, duration of clinical signs, preoperative treatment, location of the tumor, results of histologic assessment, outcome, and necropsy results was obtained from the medical record. Clients and referring veterinarians were contacted via telephone for information on recurrence of clinical signs and postoperative survival time. RESULTS: 16 dogs were > 7 years of age, and all 17 dogs had seizures before surgery. The most commonly affected breed was the Golden Retriever, represented by 6 of the 17 dogs. Median survival time was 1,254 days. Of the data collected, only histologic subtype of the tumor was prognostic. Analysis of survival times according to histologic tumor subtypes indicated that the order from most brief to longest was as follows: anaplastic, 0 days; fibroblastic, 10 days; psammomatous, > 313 days; meningothelial, > 523 days; and transitional, 1,254 days. CONCLUSIONS AND CLINICAL RELEVANCE: Use of a surgical aspirator to resect intracranial meningiomas in dogs was associated with longer survival times than those achieved with traditional surgery alone or traditional surgery combined with radiation therapy. Dogs with meningothelial, psammomatous, or transitional intracranial meningioma subtypes appeared to have a better prognosis than dogs with other subtypes of meningioma.     

Three‐dimensional conformal radiation therapy alone or in combination with surgery for treatment of canine intracranial meningiomas

Treatment protocols, treatment planning methods and tumour types in studies evaluating radiotherapy for canine brain tumours have been varied. This case series retrospectively evaluated the outcome of definitive, three‐dimensional conformal radiation therapy (3D‐CRT) as either a sole modality or as an adjuvant to surgery in 31 dogs diagnosed with meningioma by histopathology (n = 10) or cross‐sectional imaging of the head (n = 21, assessed independently by two board certified radiologists). Prescribed dose ranged from 45 to 54 Gy in 2.5 to 3 Gy fractions. Median overall survival was 577 days (interquartile range = 272–829 days; range = 30–1942 days) when all deaths were considered and 906 days (interquartile range = 336–912 days; range = 101–1942 days) when only dogs dying due to meningioma were considered. No significant difference in survival time was detected for the defined clinical or imaging findings or between treatment with radiotherapy alone versus adjuvant radiotherapy, suggesting that 3D‐CRT may be a viable alternative to surgery.     

Spinal meningiomas in dogs: Description of 8 cases including a novel radiological and histopathological presentation

Clinical, imaging, and histological features of 8 canine spinal meningiomas, including a cervical cystic meningioma with imaging and intraoperative features of an arachnoid cyst, are described. All meningiomas were histologically classified and graded following the international World Health Organization human classification for tumors. Six meningiomas were located in the cervical spinal cord. Myelography showed intradural/ extramedullary lesions in 3/4 cases. Magnetic resonance imaging revealed hyperintense intradural/extramedullary masses on pre-contrast T1-weighted and T2-weighted images with homogeneous contrast enhancement in 7/8 cases. One dog had a cerebrospinal fluid-filled subarachnoid cavity dorsal to the cervical spinal cord. A spinal arachnoid cyst was diagnosed on imaging, but the histopathological study of the resected tissue revealed a grade I meningothelial cystic meningioma. There were no differences in outcome associated with tumor grade and surgical treatment (6/8). Cystic meningioma should be considered in the differential diagnosis of intraspinal cystic lesions, and biopsy is necessary for definitive diagnosis.     

Definitive‐intent intensity‐modulated radiation therapy provides similar outcomes to those previously published for definitive‐intent three‐dimensional conformal radiation therapy in dogs with primary brain tumors: A multi‐institutional retrospective study

Radiotherapy with or without surgery is a common choice for brain tumors in dogs. Although numerous studies have evaluated use of three‐dimensional conformal radiotherapy, reports of definitive‐intent, IMRT for canine intracranial tumors are lacking. Intensity‐modulated radiation therapy has the benefit of decreasing dose to nearby organs at risk and may aid in reducing toxicity. However, increasing dose conformity with IMRT calls for accurate target delineation and daily patient positioning, in order to decrease the risk of a geographic miss. To determine survival outcome and toxicity, we performed a multi‐institutional retrospective observational study evaluating dogs with brain tumors treated with IMRT. Fifty‐two dogs treated with fractionated, definitive‐intent IMRT at four academic radiotherapy facilities were included. All dogs presented with neurologic signs and were diagnosed via MRI. Presumed radiological diagnoses included 37 meningiomas, 12 gliomas, and one peripheral nerve sheath tumor. One dog had two presumed meningiomas and one dog had either a glioma or meningioma. All dogs were treated in the macroscopic disease setting and were prescribed a total dose of 45‐50 Gy (2.25‐2.5 Gy per fraction in 18‐20 daily fractions). Median survival time for all patients, including seven cases treated with a second course of therapy was 18.1 months (95% confidence of interval 12.3‐26.6 months). As previously described for brain tumors, increasing severity of neurologic signs at diagnosis was associated with a worse outcome. Intensity‐modulated radiation therapy was well tolerated with few reported acute, acute delayed, or late side effects.     

Treatment with a combination of doxorubicin, surgery, and radiation versus surgery and radiation alone for cats with vaccine-associated sarcomas: 25 cases (1995-2000)

OBJECTIVE: To compare use of doxorubicin, surgery, and radiation versus surgery and radiation alone for treatment of cats with vaccine-associated sarcoma. DESIGN: Retrospective study. ANIMALS: 25 cats with vaccine-associated sarcomas. PROCEDURE: Time to first recurrence and survival time were compared between the 2 treatment groups. The number of surgeries (1 or > 1) were compared with respect to time to first recurrence and survival time. RESULTS: Median time to first recurrence was 661 days for the group that received doxorubicin, surgery, and radiation. Median time to first recurrence has not yet been attained for the group treated with surgery and radiation alone. Median survival time was 674 days for the group treated with doxorubicin, surgery, and radiation and 842 days for the group treated with surgery and radiation alone. For time to first recurrence and survival time, significant differences were not detected between cats that had 1 surgery and those that had > 1 surgery. CONCLUSIONS AND CLINICAL RELEVANCE: Significant differences between the 2 treatment groups were not detected. The efficacy of doxorubicin in the treatment of vaccine-associated sarcomas is uncertain.     

Occupational swine exposure and Hepatitis E virus,Leptospira, Ascaris suum seropositivity and MRSA colonization in Austrian veterinarians, 2017–2018—A cross‐sectional study

We investigated the prevalence of Hepatitis E Virus (HEV), Leptospira and Ascaris suum (A. suum) seropositivity, and of nasal methicillin‐resistant Staphylococcus aureus (MRSA) colonization among Austrian practising veterinarians, and assessed the association with occupational swine livestock exposure. The 261 participants completed a questionnaire on demographics, intensity of occupational swine livestock contact and glove use during handling animals and their secretions. Participants' blood samples were tested for HEV, Leptospira and A. suum seropositivity and nasal swabs cultured for MRSA. We compared swine veterinarians (defined as >3 swine livestock visits/week) to non‐swine veterinarians (≤3 swine livestock visits/week) with regard to the outcomes through calculating prevalence ratio (PR) and 95% confidence interval (CI). Furthermore, the relationship between occupational swine livestock contact and the study outcomes was examined by age (</≥55 years) and glove usage. The prevalence of nasal MRSA colonization was 13.4% (95% CI: 9.3–17.6), of HEV seropositivity 20.8% (95% CI: 15.8–25.7) and A. suum seropositivity 44% (95% CI: 37.7–50.2). The highest anti‐leptospiral antibodies titres were 1:200 (L. hebdomadis) and 1:100 (L. autumnalis, L. caicola) found in three non‐swine veterinarians. Compared to non‐swine veterinarians, swine veterinarians were 1.9 (95% CI: 1.0–3.4) and 1.5 (95%CI: 1.0–2.3) times more likely HEV seropositive and A. suum seropositive, respectively, and 4.8 (95%CI: 2.5; 9.3) times more likely nasally colonized with MRSA. Among glove‐using veterinarians, occupational swine contact was no longer a determinant for HEV seropositivity (PR 1.6; 95% CI: 0.8–2.9). Similar was found for A. suum seropositivity, which was no longer associated with occupational swine livestock contact in the subgroup of glove using, ≥55‐year‐old veterinarians (PR: 1.07; 95% CI: 0.4–3.3). Our findings indicate that >3 occupational swine livestock visits per week is associated with HEV and A. suum seropositivity and nasal MRSA colonization and that glove use may play a putative preventive role in acquiring HEV and A. suum. Further analytical epidemiological studies have to prove the causality of these associations.     

Linac‐based stereotactic radiation therapy for canine non‐lymphomatous nasal tumours: 29 cases (2013‐2016)

Twenty‐nine dogs were treated with linac‐based stereotactic radiation therapy (SRT) for non‐lymphomatous nasal tumours. Only dogs with a follow‐up time >365 days were included in this retrospective analysis. No dogs had evidence of distant metastasis at diagnosis. Treatment was planned and a total of 30 Gy in 3 daily 10 Gy fractions was delivered using intensity‐modulation, cone‐beam CT‐based image guidance and a robotic treatment couch. Clinical signs improved in all cases. Nineteen dogs had CT scans 3‐4 months post‐SRT and all had partial or complete tumour response. Minimal acute toxicities were detected. Clinically significant late toxicities included oronasal or nasocutaneous fistulas (N = 3) and biopsy‐confirmed fungal rhinitis with no evidence of tumour progression (N = 2). The median progression‐free survival (PFS) was 354 days, with 49% and 39% progression‐free at 1 and 2 years post‐SRT, respectively. The median survival time (ST) was 586 days, with 69% and 22% alive 1 and 2 years post‐SRT, respectively. Neither the clinical parameters evaluated (modified Adams’ stage, histopathology, presence of intracranial extension of the tumour) nor dosimetric data were predictive for PFS or ST. This SRT protocol appears to be well tolerated, and PFI and ST are comparable or superior to those reported in other definitive‐intent radiotherapy protocols.     

Clinical features and outcome of dermal squamous cell carcinoma in 193 dogs (1987‐2017)

Squamous cell carcinoma (SCC) is a frequently recognized dermal tumour in dogs and has been described as a common pathology induced by solar ultraviolet radiation exposure. Little has been published about this neoplasm with regard to clinical features and outcome in dogs. This retrospective study included 193 dogs from a single institution histopathologically diagnosed with SCC of the dermis. Thirty‐eight percent of all dogs had documented histopathologic actinic change. The overall median survival time was 1004 days, with the population demonstrating actinic change associated with a significantly longer survival time (median 1359 days, range 16‐3530 days) compared to dogs without actinic change (median 680 days, range 16‐3066 days) and this achieved significance on multivariate analysis (hazard ratio 0.42, 95% confidence interval 0.193‐0.930, P = 0.032). These data demonstrate increased survival of dogs with SCC demonstrating actinic change over those with non‐actinic SCCs, and purports long‐term survival for these animals. Dogs received a variety of treatment approaches as a retrospective study, and future prospective studies will be necessary to investigate whether adjunct therapies such as radiation or chemotherapy offer improvement in survival for dermal SCC in the dog.     

Efficacy of stereotactic radiation therapy for the treatment of confirmed or presumed canine glioma

Intracranial gliomas are the second most common brain tumour in dogs. Radiation therapy provides a minimally invasive treatment option for this tumour type. Earlier publications reporting on the use of non-modulated radiation therapy suggested a poor prognosis for dogs with glioma, with median survival times ranging between 4 and 6 months; more recent literature utilizing stereotactic radiation therapy (SRT) demonstrates that the prognosis for canine gliomas may be more promising, with survival times closer to 12 months. A single institution retrospective study was performed between 2010 and 2020 investigating the outcomes of dogs with biopsy-confirmed glioma or a presumptive diagnosis of intra-cranial glioma based on MRI characteristics that were treated with SRT. Twenty-three client-owned dogs were included. Brachycephalic breeds were overrepresented, totalling 13 dogs (57%). SRT protocols included 16 Gy single fraction (n = 1, 4%), 18 Gy single fraction (n = 1, 4%), 24 Gy in 3 daily fractions (n = 20, 91%), or 27 Gy in four daily fractions (n = 1, 4%). Twenty-one dogs (91%) had improvement of their presenting clinical signs following SRT. Median overall survival time (MST) was 349 days (95% CI, 162–584). Median disease specific survival time was 413 days (95% CI, 217–717). When SRT is incorporated into the management plan for dogs with confirmed or presumed intracranial glioma, a median survival time of approximately 12 months may be achievable.     

Surgery alone or in combination with radiation therapy for treatment of intracranial meningiomas in dogs: 31 cases (1989-2002)

OBJECTIVE: To compare, for dogs with intracranial meningiomas, survival times for dogs treated with surgical resection followed by radiation therapy with survival times for dogs treated with surgery alone. DESIGN: Retrospective study. ANIMALS: 31 dogs with intracranial meningiomas. PROCEDURE: Medical records of dogs with histologic confirmation of an intracranial meningioma were reviewed. For each dog, signalment, clinical signs, tumor location, treatment protocol, and survival time were obtained from the medical record and through follow-up telephone interviews. RESULTS: Dogs that underwent tumor resection alone and survived > 1 week after surgery had a median survival time of 7 months (range, 0.5 to 22 months). Dogs that underwent tumor resection followed by radiation therapy had a median survival time of 16.5 months (range, 3 to 58 months). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that in dogs with intracranial meningiomas, use of radiation therapy as a supplement to tumor resection can significantly extend life expectancy.     

Evaluation of outcome associated with subcutaneous and intramuscular hemangiosarcoma treated with adjuvant doxorubicin in dogs: 21 cases (2001-2006)

OBJECTIVE: To evaluate outcome associated with subcutaneous and intramuscular hemangiosarcomas treated with adjuvant doxorubicin in dogs. DESIGN: Retrospective case series. ANIMALS: 21 dogs. PROCEDURES: Records of dogs with histologically confirmed hemangiosarcoma, no detectable metastasis at initial evaluation, and adequate local tumor control were included. Age, sex, number of treatments, treatment interval, radiation therapy, and concurrent use of cyclophosphamide or deracoxib were evaluated for associations with disease-free interval (DFI) or survival time. Three to 6 cycles of doxorubicin were planned. Disease-free interval was defined as time of definitive surgery to time of local recurrence, metastasis, or both. Survival time was defined as the beginning of the DFI to time of death. RESULTS: 17 tumors were subcutaneous, and 4 were intramuscular. Median age was 9 years. Median weight was 31.1 kg (68.4 lb). Five dogs received adjuvant radiation therapy. Median DFI for subcutaneous tumors was 1,553 days (95% confidence interval [CI], 469 days to not estimable). Median DFI for intramuscular tumors was 265.5 days (95% CI, 123 to 301 days). Median survival time for subcutaneous tumors was 1,189 days (95% CI, 596 days to not estimable). Median survival time for intramuscular tumors was 272.5 days (95% CI, 123 to 355 days). For dogs with subcutaneous tumors, younger age (< 9 years) was associated with longer DFI and survival time. Dogs with subcutaneous tumors that did not receive radiation therapy had longer DFI. CONCLUSIONS AND CLINICAL RELEVANCE: Dogs with subcutaneous hemangiosarcoma had a more favorable outcome, compared with dogs with intramuscular hemangiosarcoma, when treated with adequate local control and adjuvant doxorubicin.     

Treatment outcomes and target delineation utilizing CT and MRI in 13 dogs treated with a uniform stereotactic radiation therapy protocol (16 Gy single fraction) for pituitary masses: (2014‐2017)

Canine pituitary tumours are increasingly treated with stereotactic radiotherapy (SRT). Here, we report clinical outcomes in dogs treated with single‐fraction SRT; we also explore technical aspects of SRT treatment planning. A single‐institution retrospective study was performed, including any dog with a pituitary mass (PM) that was treated using a standardized single‐fraction (16 Gy) SRT protocol between 2014 and 2017. Via medical records review, 13 cases were identified. Nine dogs neurologically improved after SRT. Four dogs experienced MRI‐documented tumour volume reduction. Nine dogs experienced neurologic decline in 1.5 to 18 months after SRT and were euthanized. The median overall survival time was 357 days, with 15% alive 18 months after SRT. To better understand whether SRT target delineation is predictably altered by use of magnetic resonance imaging (MRI) in addition to computed tomography (CT), two radiation oncologists (RO) retrospectively re‐evaluated all imaging studies used for SRT planning in these 13 cases. Gross tumour volume (GTV) was contoured on co‐registered CT and MRIs for each case. In seven cases, CT alone was deemed inadequate for GTV contouring by at least one RO. T1 post‐contrast MRI was considered the ideal image for GTV contouring in 11 cases. Contouring on MRI yielded larger GTV than CT for 11 cases. Inter‐observer variability existed in each case and was greater for MRI. In summary, use of co‐registered CT and MRI images is generally considered advantageous for PM delineation when using SRT. Notably, survival times reported herein are shorter than what has previously been reported for PM treated with finely fractionated full‐course RT protocols.     

RETROSPECTIVE COMPARISON OF THREE‐DIMENSIONAL CONFORMAL RADIATION THERAPY VS. PREDNISOLONE ALONE IN 30 CASES OF CANINE INFRATENTORIAL BRAIN TUMORS

Infratentorial tumors are relatively infrequent in dogs and a lack of data makes it difficult to offer prognostic information. Untreated, dogs with these neoplasms have shorter survival times than those with supratentorial tumors. The role of radiation therapy (RT) in the management of infratentorial tumors is poorly defined and tumoral/peritumoral swelling in this site is a potential cause of serious acute side effects. The aim of this retrospective, cohort study was to describe cases of infratentorial tumors treated with fractionated three‐dimensional conformal RT (3D CRT) and glucocorticoids (GC), and compare outcomes and survival with dogs affected by tumors in the same location that received GC alone. Thirty patients with a MRI diagnosis of infratentorial tumors were recruited (15 received RT and GC and 15 GC alone). None had mentation changes at presentation. For both groups, MRI and medical records were reviewed; and factors associated with survival were evaluated with Kaplan–Meier product limit survival and Cox regression analysis. Overall median survival time (MST) was 294 days (95% CI 42–545). The MST in the RT group was 756 days (95% CI 209–1302) vs. 89 days (95% CI 34.7–143.3 days) for those dogs treated palliatively with GC alone. This difference was statistically significant (P = 0.001). No other factors (including neurological signs, MRI features, tumor volume and total RT dose) were statistically associated with survival in the RT group. This study suggests that 3D CRT offers a survival advantage for dogs with infratentorial tumors compared to GC alone, and significant complications are uncommon.     

Long‐term outcomes with conventional fractionated and stereotactic radiotherapy for suspected heart‐base tumours in dogs

Published radiotherapy results for suspected heart‐based tumours in dogs are limited. In this retrospective longitudinal study (3/2014‐2019), eight dogs with either clinical signs attributable to a heart‐base mass (6), or asymptomatic with a progressively larger mass on echocardiogram (2), received conventional fractionated radiotherapy (CFRT) or stereotactic body radiotherapy (SBRT). Clinical findings in symptomatic cases included one or more of the following: retching/coughing (4), exercise intolerance (2), collapse (1), pericardial effusion (2), rare ventricular premature contractions (2), abdominal effusion (1), or respiratory distress due to chylothorax (1). CFRT cases received 50 Gray (Gy) in 20 fractions and SBRT cases received 30 Gy in 5 or 24 Gy in three fractions. Two dogs received chemotherapy post‐radiation. At analysis, 7/8 dogs were deceased and one was alive 684 days post‐treatment. The estimated median overall survival (MOS) from first treatment was 785 days (95% CI 114‐868 days, [range 114‐1492 days]). Five dogs received CFRT (MOS 817 days; (95% CI 155 days‐not reached [range 155‐1492 days])). Three dogs received SBRT with one alive at analysis (MOS 414 days, (95% CI, 114 days‐not reached [range 114‐414 days])). No statistically significant difference was found between survival for CFRT and SBRT. Of the symptomatic patients, 5/6 showed improvement. Mass size reduced in 4/5 cases receiving follow‐up ultrasounds. Possible complications included asymptomatic radiation pneumonitis (4), atrial tachycardia/premature beats (4) and pericardial effusion with heart failure coincident with tumour progression (1). This study provides preliminary evidence that radiotherapy may impact clinically relevant or progressively enlarging heart‐base masses.     

Comparison between symptomatic treatment and lomustine supplementation in 71 dogs with intracranial,space‐occupying lesions

Brain neoplasia is diagnosed in an increasing number of dogs. Consequently, there is a higher need for an effective treatment. Chemotherapy is considered in cases where surgery or radiation is not optional. The objective of this retrospective study was to evaluate the difference in median survival time (MST) of dogs with intracranial masses, treated symptomatically with corticosteroids and anti‐epileptic drugs, compared with the same symptomatic treatment supplemented with lomustine. The records of 71 dogs with intracranial masses were retrospectively evaluated. Fifteen dogs were treated symptomatically with corticosteroids and anti‐epileptics, and 56 dogs received additional therapy with lomustine. There was no statistically significant difference in MST between both groups, being 60 and 93 days, respectively. Age, duration of symptoms, intracranial localization of the mass and intra‐ or extra‐axial localization had no influence on survival time. However, female dogs survived significantly longer than male dogs.     

Long‐term survival with stereotactic radiotherapy for imaging‐diagnosed pituitary tumors in dogs

Published studies on the use of stereotactic radiotherapy for dogs with pituitary tumors are limited. This retrospective observational study describes results of stereotactic radiotherapy for 45 dogs with imaging‐diagnosed pituitary tumors. All dogs were treated at a single hospital during the period of December 2009–2015. The stereotactic radiotherapy was delivered in one 15 Gray (Gy) fraction or in three 8 Gy fractions. At the time of analysis, 41 dogs were deceased. Four were alive and censored from all survival analyses; one dog received 8 Gy every other day and was removed from protocol analyses. The median overall survival from first treatment was 311 days (95% confidence interval 226–410 days [range 1–2134 days]). Thirty‐two dogs received 15 Gy (median overall survival 311 days; 95% confidence interval [range 221–427 days]), and 12 received 24 Gy on three consecutive days (median overall survival 245 days, 95% confidence interval [range 2–626 days]). Twenty‐nine dogs had hyperadrenocorticism (median overall survival 245 days), while 16 had nonfunctional masses (median overall survival 626 days). Clinical improvement was reported in 37/45 cases. Presumptive signs of acute adverse effects within 4 months of stereotactic radiotherapy were noted in 10/45, and most had improvement spontaneously or with steroids. Late effects versus tumor progression were not discernable, but posttreatment blindness (2), hypernatremia (2), and progressive neurological signs (31) were reported. There was no statistical difference in median overall survival for different protocols. Patients with nonfunctional masses had longer median overall survival than those with hyperadrenocorticism (P = 0.0003). Survival outcomes with stereotactic radiotherapy were shorter than those previously reported with definitive radiation, especially for dogs with hyperadrenocorticism.     

Use of real‐time quantitative PCR to document successful treatment of Mycoplasma haemocanis infection with doxycycline in a dog

An 8‐year‐old Jack Russell Terrier was diagnosed with hemolytic anemia caused by hemoplasmosis 4 years following splenectomy. Quantitative real‐time PCR (qPCR) analysis was used initially to confirm infection with Mycoplasma haemocanis and subsequently to monitor and direct medical therapy. Doxycycline was administered beyond resolution of clinical signs until hemoplasma DNA could no longer be detected by qPCR. The dog remained clinically healthy and hemoplasma‐negative 8 months following cessation of therapy. Canine hemoplasmosis should remain as a differential diagnosis for hemolytic anemia in dogs, particularly those that are splenectomized or immunocompromised, even in geographic regions where prevalence of infection is low. Prolonged doxycycline administration has been shown by qPCR to lead to sustained absence of detectable infection and should be considered as a first line treatment for canine hemoplasmosis.     

Patient characteristics,prognostic factors and outcome of dogs with high‐grade primary mediastinal lymphoma

The goals of this retrospective study were to determine the patient characteristics of dogs with high‐grade primary mediastinal lymphoma and to determine outcome and associated prognostic factors. A total of 42 dogs were identified, in which 36 received treatment and had follow‐up information available. The most common clinical signs included lethargy, anorexia and polyuria/polydipsia. Hypercalcemia and pleural effusion were common findings at diagnosis. The phenotype was almost exclusively T‐cell, most often in association with lymphoblastic cytomorphology as defined by the World Health Organization (WHO) lymphoma classification scheme. The overall progression‐free survival (PFS) and overall survival (OS) were 133 and 183 days, respectively. Treatment with a CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone) protocol was associated with an improved PFS (144 days) and OS (194 days) when compared with dogs that received other medical therapies (P = .005 and P = .002, respectively); the absence of pleural effusion at diagnosis was associated with an increased OS but not PFS. These results suggest that while the prognosis for dogs with mediastinal lymphoma is poor, survival may be improved with treatment using a CHOP‐based protocol.