What if the Pet Owner Won’t go for Oncology Referral?

By Chelsea Greenberg, DVM, MS, Diplomate ACVIM (oncology)

Millions of dogs and cats are diagnosed with cancer each year. Although interest in oncology referral is growing, some pet owners will elect against it. The reasons for referral refusal are varied. Presumptions or misconceptions about pain and suffering during cancer therapy, concern about costs for treatment, or level of emotional attachment to their pet are a few common reasons that pet owners decline referral. 

If a pet owner declines referral and you end up managing the case, it’s important to remember that oncology can be both challenging and rewarding. Two-way communication between the hospital team and pet owner is essential for optimal patient care. Current cancer recommendations change rapidly, and clients are becoming more internet savvy so be sure to research treatment options before discussing a plan with the client. Depending on the treatment options you will offer, be sure to have adequate safety protocols in place for the patient, you, and your staff.

Basics of cancer therapy:

Cancer therapy is not the same as it was 15, or even 5 years ago. Rapid advancements in understanding cancer biology and the immune system have increased the options that are now available for veterinary patients.

Although treatment options are increasing, cancer therapy recommendations differ depending on the goals of the client (cure, control (extending quality of life), or palliation). Starting a conversation with the client regarding their goals before presenting treatment options will allow those treatment options to better meet the client’s expectations. It is the attending veterinarian’s responsibility to make sure that the client has adequate information about available cancer treatment options which will improve patient care. When surveyed, clients had the expectation to be supported by their veterinarian when making informed decisions. Pet owners expected the veterinarian to understand their current knowledge base, tailor information to their needs, and educate them about their options [1]. A more in-depth look at client communication will be addressed in a future blog.

Treating cancer:

Declining the referral will limit the number of treatment options available, yet many options are still available in general practice. Even so, it’s best to only use cancer treatment options in your practice that you are comfortable with and can implement safely.

Surgery

If the intent of surgery is curative, the first chance to “cut” is the chance to cure. Once the mass has been removed the first time, anatomy will be forever changed. Surgical trauma (undermining tissue, etc.) and the body’s normal healing processes (tissue contracture/scar tissue) are both contributors to these anatomic disruptions.  Tissue disruption, including placement of surgical drains, allows residual cancer cells to travel to areas they may not have had access to prior and/or stimulate further growth. Curative surgery requires careful and thorough planning (complete and adequate margins). No cancer treatment modality (additional surgery, radiation therapy, chemotherapy, or immunotherapy) can salvage a patient from a poorly planned and/or executed surgery.

Surgery can also be palliative (non-curative) to help with patient comfort – such as amputation for presumptive osteosarcoma or moderate margins for a larger soft tissue sarcoma. Cytoreduction of oral masses can help increase nutritional intake and may temporarily decrease pain.

Medical therapy 

Chemotherapy – Although many chemotherapy drugs are given intravenously, there are oral options that use angiogenesis inhibition and decrease T regulatory cell populations to help control cancer growth [2, 3]. This type of chemotherapy is known as metronomic chemotherapy and is given orally in small daily doses. Cyclophosphamide, chlorambucil, and non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used drugs in metronomic chemotherapy protocols [4]. Metronomic chemotherapy usually requires less monitoring than other types of chemotherapy which minimizes hospital visits.  However metronomic chemotherapy may expose pet owners to hazardous drugs by handling the tablets or capsules and from the pet’s urine or feces.

Immunotherapy

Immunotherapy is quickly becoming the fourth pillar of cancer treatment, alongside surgery, radiation therapy, and chemotherapy. There are multiple types of immunotherapies: cancer vaccines, monoclonal antibodies, oncolytic viruses, checkpoint inhibitors, and adoptive cell therapies. A type of cancer vaccine called an autologous cancer vaccine (ACV) is currently available to specialists and general practitioners as an experimental therapeutic under USDA regulations. This ACV vaccine (Torigen® autologous cancer vaccine; ACV-T) works to recruit the patient’s own immune system as the source of antigens is derived from the patient’s cancer cells. ACV-T presents the immune system with a large menu of tumor-associated and tumor-specific antigens that are unique to the individual animal, along with an adjuvant to activate the immune system. ACV-T is given subcutaneously once weekly for 3 total doses in small animals (6 doses in horses) and appears to be well tolerated in cats, dogs, and horses [5-7]. The anticancer effects of the ACV-T have been demonstrated in rodent models and in dogs with metastatic hemangiosarcoma [8-10]. Additional veterinary clinical studies are underway.

Cancer treatment tips:

Do not have the same expectations for cancer treatment as you would other diseases (such as cardiac or endocrine disease) as not all cancers will respond as anticipated, even if you do all the “right” things. Cancer is a complex disease process and can be unpredictable. For example, just because the last 2 oral melanomas you treated responded to carboplatin doesn’t mean the 3rd one will respond.

Cancer treatments need time to work. Outside of surgery and a few very specific diagnoses (such as CHOP chemotherapy for high-grade lymphoma), cancer treatment can take several weeks before you see a response. If a patient is ill from the cancer, they may not have weeks to wait for quality-of-life improvement. Clear communication with the client sets up proper expectations and can also influence treatment decisions.

Treating the whole patient:

Cancer management is not just about what we can do about the cancer, but what can we do for the whole patient. Regardless of cancer response to treatment, it is important to make sure that our patients are comfortable.

Pain management

Treating pain or discomfort is paramount. Even if a mass is not directly painful upon palpation during physical examination, the pet may still be experiencing pain (such as with chewing, or weight-bearing). Clients often worry that their pet is in pain. Client feedback can be very helpful in estimating pain levels as your patient will often be more relaxed in the home environment. There are different types of pain, acute and chronic. The cancer patient may experience more than one of these types of pain at one time. Acute pain is often from tissue injury, such as a biopsy, or surgery and this type of pain will dissipate as tissue heals. Chronic pain is the hardest to identify in pets and is a result of pain being unchecked, either constant or intermittent. As pain continues, the central nervous system becomes rewired leading to central sensitization, hyperalgesia, allodynia and wind-up pain [11]. Chronic pain is often due to a health condition, such as the cancer itself and/or arthritis. Neuropathic pain is a common type of chronic pain which arises from nerve damage or compression. This type of chronic pain can come from the cancer as well as from unrelated causes such as intervertebral disk disease. Neuropathic pain can interfere with normal movement and cause mobility issues.

Cancer patients suffering from pain, both acute and chronic, often benefit from combination pain management. Combination pain management is most beneficial when the individual medications act through different analgesic pathways. This provides more effective pain relief with lower dosages of each medication which can decrease the chances of undesirable side effects (sedation or gastrointestinal upset). Effective combinations may include NSAIDs, opioids, N-methyl-D-aspartate receptor antagonists (amantadine), and gabapentinoids. Bisphosphonates, such as zoledronate, are useful for managing pain arising from primary or metastatic bone tumors and can be used with medication combinations described above. Stay tuned for a more detailed blog about pain management for veterinary cancer patients.

Nutritional support

Maintaining nutritional balance can be difficult in cancer patients, especially cats. Pain, discomfort, and concurrent medications may diminish appetite. Cancers affecting the oral cavity and gastrointestinal tract can also cause mechanical difficulties with chewing and digesting food. Gastric ulceration can occur from histamine release from mast cell tumors.

If the patient has lost weight, coach the clients to provide high quality, tasty, calorie dense foods. If oral food intake is not enough to support proper nutrition, enteral feedings can be considered and may facilitate medication administration. A common method of enteral supplementation is with an esophagostomy tube. Placement is straightforward, and the tube diameter is typically large enough to efficiently provide ample calories. Although nasogastric tubes are easy to place, the small-bore size limits the number of daily calories and can be irritating for the patient. Gastrostomy tubes are the largest diameter which is excellent for medication administration and feeding a significant daily volume. However, placement of these tubes requires endoscopic guidance or surgery.

Many cancer patients will experience nausea during their disease process as either a direct influence of the cancer, or indirectly from concurrent medications. There are a variety of antiemetics that are available for veterinary patients. Maropitant (Cerenia®) is a potent centrally active antiemetic that can also decrease pain and inflammation through inhibition of the NK-1 pathway. Maropitant is available in injectable and oral formulations and addresses nausea and vomiting in multiple clinical scenarios. Ondansetron (Zofran®) is a serotonin 5-HT3 receptor antagonist that is also available in injectable and oral formulations for a wide variety of clinical applications.

Appetite stimulants should only be used after addressing any underlying medical causes that may affect appetite. In veterinary cancer patients, a decreased appetite is often the result of discomfort or nausea rather than behavioral. It is imperative to treat these potential underlying causes before using appetite stimulants. Do not force a pet to eat when they are uncomfortable or nauseated, as food aversion can be learned and is difficult to overcome.

Common appetite stimulants for dogs and cats include capromorelin (Entyce™/Elura™), mirtazapine, and cyproheptadine. Capromorelin is a ghrelin receptor agonist that causes an increase in growth hormone thus stimulating appetite. Mirtazapine is a serotonin 5-HT2c and histamine1 receptor antagonist that blocks appetite inhibition and has less frequent dosing in cats (every 2-3 days) which may be an advantage for some clients. Cyproheptadine is an antihistamine that also has serotonin-antagonist action and appears to be more beneficial in cats than dogs. Glucocorticoids can also stimulate appetite; however, they do not provide analgesia. Reconsider using glucocorticoids for appetite stimulation if NSAIDs are part of the patient’s pain management regimen.

Even if your client declines the oncology referral, clear communication, providing treatment and supporting the pet in your practice can be rewarding for the client, you, and your staff. Offering care that would otherwise not be available will help strengthen the relationship between your team and the pet owner and ultimately improve the quality of life of your patient.

1. Janke N, Coe JB, Bernardo TM, Dewey CE, Stone EA: Pet owners’ and veterinarians’ perceptions of information exchange and clinical decision-making in companion animal practice. PLoS One 2021, 16(2):e0245632.

2. Hanahan D, Bergers G, Bergsland E: Less is more, regularly: metronomic dosing of cytotoxic drugs can target tumor angiogenesis in mice. J Clin Invest 2000, 105(8):1045-1047.

3. Elmslie RE, Glawe P, Dow SW: Metronomic Therapy with Cyclophosphamide and Piroxicam Effectively Delays Tumor Recurrence in Dogs with Incompletely Resected Soft Tissue Sarcomas. J Vet Intern Med 2008, 22(6):1373-1379.

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9. Suckow MA, Wolter WR, Sailes VT: Inhibition of prostate cancer metastasis by administration of a tissue vaccine. Clin Exp Metastasis 2008, 25(8):913-918.

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