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The management of apocrine gland anal sac adenocarcinoma (ASAC) presents a distinct challenge when owners decline specialist referral. This case describes the management of a recurrent ASAC in a cavoodle using toceranib phosphate (Palladia) in a general practice setting.
A protocol of surgical excision and maintenance tyrosine kinase inhibitor (TKI) therapy achieved 14 months of clinical remission and a total survival time currently exceeding four years from initial diagnosis, demonstrating the viability of accessible advanced medical management in primary care.
Case presentation
Dexter, an eight-year-old male neutered cavoodle weighing 9.4kg presented for routine dental prophylaxis. During the pre-anaesthetic physical examination, a 3mm firm perirectal mass was detected adjacent to the right anal gland.
Fine needle aspiration cytology revealed a round cell population consistent with neuroendocrine neoplasia. Pre-operative staging with computed tomography (CT) at a referral centre confirmed the absence of metastatic disease. Surgical excision confirmed ASAC via histopathology; however, margins were narrow (deep <1 mm, lateral 0.1 mm), and complete excision could not be guaranteed.
The owners were counselled regarding adjuvant chemotherapy and radiation therapy but declined referral. A protocol of active surveillance was instituted with three-monthly monitoring. Eighteen months later, routine digital rectal examination detected a firm 2.5 x 1cm mass at the original surgical site. Repeat staging, including thoracic radiography and abdominal ultrasonography, remained unremarkable for distant metastasis.
The owners again declined referral for radiation therapy citing financial constraints and a desire to minimise hospital time for Dexter. A second surgical excision was performed in general practice. Post-operative recovery was complicated by transient faecal incontinence, which resolved within two weeks with supportive care. Histopathology confirmed recurrent ASAC with margins <0.5mm.
Within months, a third recurrence occurred with rapid local progression. Given the risk of permanent faecal incontinence associated with a third surgery, further intervention was deemed inadvisable. The goal of therapy shifted from ‘cure’ to ‘realistic disease control’, prioritising quality of life.
Several medical options exist for ASAC when surgery is not elected. Traditional chemotherapy agents such as carboplatin and actinomycin-D have demonstrated partial response rates of 33%1 to 50%5, though these figures derive from small study populations. Radiation therapy can achieve clinical improvement in up to 63% of cases in gross disease settings7, but access and cost remain significant barriers for many clients.
Toceranib phosphate (Palladia), a multi-kinase inhibitor targeting vascular endothelial growth factor receptor 2 (VEGFR-2), platelet-derived growth factor receptor (PDGFR), KIT, and other receptors expressed in canine ASAC10, offers a more accessible option.
Published data indicate clinical benefit in approximately 69% of dogs with ASAC6, with around 21% achieving partial response and 48% achieving stable disease. Importantly, stable disease is considered a therapeutic success when quality of life is maintained. Lower-dose protocols (2.4–2.9 mg/kg every other day) maintain target inhibition while reducing adverse effects compared to label dosing2.
Setting expectations: client communication
Transparent communication was pivotal to the owner’s consent and ongoing compliance. The conversation addressed:
• Treatment goals: The owners understood that toceranib would not cure Dexter’s cancer. The aim was to arrest tumour growth and maintain quality of life for as long as possible.
• Timeline: Because toceranib does not directly kill cancer cells but rather inhibits tumour blood supply and growth signals, responses can take 6–12 weeks to become apparent. This requires patience and trust from owners.
• Adverse effects: We discussed the potential for gastrointestinal toxicity (20–40% of cases), myelosuppression, hypertension, proteinuria, and less common effects including hepatopathy, shifting lameness, and pancreatitis2, 3. Early intervention allows dose adjustment before complications escalate.
• Financial commitment: Monthly medication costs were estimated at AUD $300–400, with monitoring fees of approximately AUD $150–250/month. Critically, we explained that toceranib is a lifelong therapy for as long as it maintains remission.
• Safe handling: As an oral chemotherapy agent administered at home, safe handling practices were reviewed.
• Decision criteria: We established clear criteria for continuing therapy; treatment would proceed as long as Dexter experienced no significant side effects and maintained good quality of life.
Treatment
Dexter commenced toceranib at a target dose of ~2.7 mg/kg rounded to the nearest whole tablet combination: 25 mg every 48 hours (2.65 mg/kg actual; 10 mg + 15 mg tablets).
Monitoring was rigorous to ensure safety. Weeks 1–2 involved telephone follow-up and initial bloodwork (CBC, biochemistry). Months 1–3 required monthly CBC and biochemistry. Ongoing monitoring comprised eight-weekly CBC and biochemistry, with monthly digital rectal examination and urinalysis. Comprehensive biochemistry differentiated drug toxicity from concurrent disease. Blood pressure was monitored via oscillometry to screen for hypertension, and urinalysis monitored for protein-losing nephropathy9.
Within three weeks, mass growth was arrested. By six weeks, the mass was non-palpable on rectal examination. Dexter enjoyed 14 months of complete clinical remission. One published paper4 reported a median progression-free interval of 354 days in dogs with stage 4 (metastatic) ASAC treated with toceranib. Dexter’s disease at treatment initiation was locally recurrent without confirmed distant metastases—a potentially more favourable prognostic category, so this response duration was within expected parameters.
Adverse effects were minimal. Two episodes of loose stools associated with dietary indiscretion were managed with a brief 4-day treatment interruption. Mild intermittent leucopenia and Grade 1 neutropenia normalised spontaneously without dose reduction. No evidence of proteinuria or hypertension was detected.
This case illustrates the potential for general practitioners to achieve good outcomes in managing recurrent ASAC. The total survival time from initial diagnosis currently exceeds 52 months, achieved through a combination of surgery and targeted medical therapy.
While Dexter represents a favourable scenario, his case is supported by the broader literature confirming that clinical benefit is achievable in the majority of treated dogs8. Critically, this highlights the potential for general practitioners to deliver advanced oncological care. Tools like Palladia enable GPs to offer viable alternatives to euthanasia or referral when owners decline or cannot access specialist services.
Three years since Dexter initially presented for the dental procedure, a recurrence of ASAC was detected. Consistent with the palliative goals established at the outset, the owners declined further staging. Management now focuses on maintaining Dexter’s comfort, closing the circle on a successful, extended period of quality life.
Key messages
Toceranib phosphate offers a viable medical management option for recurrent ASAC when further surgery carries unacceptable risks or owners decline referral. Rigorous monitoring, particularly for silent sequelae like hypertension and proteinuria, is essential for safe long-term use in general practice. Transparent communication about costs, adverse effects, and realistic expectations is critical to informed owner consent and successful case management.
References
1. Bennett PF, DeNicola DB, Bonney P, Glickman NW, Knapp DW. Canine anal sac adenocarcinomas: clinical presentation and response to therapy. J Vet Intern Med. 2002;16(1):100-104.
2. Bernabe LF, Portela R, Nguyen S, et al. Evaluation of the adverse event profile and pharmacodynamics of toceranib phosphate administered to dogs with solid tumors at doses below the maximum tolerated dose. BMC Vet Res. 2013;9:190.
3. Brown DC, et al. Preliminary evidence for biologic activity of toceranib phosphate (Palladia®) in solid tumours. BMC Vet Res. 2012;8:14.
4. Elliott J. Response and outcome following toceranib phosphate treatment for stage four anal sac apocrine gland adenocarcinoma in dogs: 15 cases (2013-2017). J Am Vet Med Assoc. 2019;254(8):960-966.
5. Hammer AS, Couto CG, Ayl RD, Shank KA. Treatment of tumor-bearing dogs with actinomycin D. J Vet Intern Med. 1994;8(3):236-239.
6. Heaton CM, Fernandes AFA, Jark PC, Pan X. Evaluation of toceranib for treatment of apocrine gland anal sac adenocarcinoma in dogs. J Vet Intern Med. 2020;34(2):873-881.
7. McQuown B, Keyerleber MA, Rosen K, et al. Treatment of advanced canine anal sac adenocarcinoma with hypofractionated radiation therapy: 77 cases (1999–2013). Vet Comp Oncol. 2017;15(3):840–851.
8. Morey J, Brockley L. Toceranib phosphate for treatment of hypercalcaemia of malignancy in two dogs with metastatic anal sac apocrine gland adenocarcinoma. N Z Vet J. 2025;73(5):337-344.
9. Tjostheim SS, Stepien RL, Markovic LE, Stein TJ. Effects of toceranib phosphate on systolic blood pressure and proteinuria in dogs. J Vet Intern Med. 2016;30(4):951-957.
10. Urie BK, Russell DS, Kisseberth WC, London CA. Evaluation of expression and function of vascular endothelial growth factor receptor 2, platelet derived growth factor receptors-alpha and -beta, KIT, and RET in canine apocrine gland anal sac adenocarcinoma and thyroid carcinoma. BMC Vet Res. 2012;8:67.
Dr Daniel Richmond BSc BVMS
Dr Daniel Richmond graduated from Murdoch University in 1995 and practised in the UK and Australia for three decades.
A previous practice owner, Dr Richmond is now a lead veterinarian at Willunga and Aldinga Veterinary Services in SA where he mentors early-career veterinarians in complex medicine and imaging.
Observing the impact of communication on veterinary burnout, Dr Richmond co-founded Vet Detective, a training consultancy teaching veterinarians how to navigate difficult client conversations.
