Weeks 7 and 8: Medical Oncology!

Medical oncology rotation is now in the books! These two weeks were incredibly insightful as to what the world of veterinary medical oncology entails. Prior to this rotation, I had very little experience in oncology and had developed my own mental model of what this field encompassed. Spoiler alert, as you may suspect, the rotation totally reframed my mindset.

The oncology team at UC Davis was packed full of some of the sweetest humans I have ever met in my life. From the receptionists to the technicians, residents, and doctors, the whole team was incredibly cheery and always willing to teach. They welcomed all of us with open arms and created a safe place to learn and ask questions. I immediately felt safe on this rotation and knew that I wouldn’t be judged for not knowing something.

In terms of hours and expectations, medical oncology is fairly tame. Most days start around 8:00 with topic rounds where we have the chance to dive deeper into a specific type of cancer. This is a nice way to build upon knowledge from the first three years of didactic learning and then apply it to cases and look into specific treatment plans. We also had the chance to dive into a lot of current literature regarding treatment protocols, which was helpful! After the conclusion of our rounds sessions, we would head to the treatment room to “run the board”. This was where each resident briefly presented their cases for the day so that everyone on the team was on the same page. Most days consisted of a plethora of chemo patients or recheck appointments coupled with a few new appointments.

This rotation allows the students to choose their case the night before so that the evening could be used to prepare for the following day. Most of the time, we were given the new patients so that we could participate in the full workup procedure, including laboratory work and imaging such as thoracic rads, abdominal ultrasound, or CT. On Fridays, there are no new appointments, so we are all given a recheck case, and this is usually when we get to help administer chemotherapy.

Every day ends with a rounds discussion, which usually begins around 4:00. This is a chance for us to meet as a team and debrief all the new cases. The students present the case, diagnostics, and plan for the patient, and then we talk as a team to flush out any points of the case that were confusing or foundational learning points. I found these sessions to be incredibly helpful and always walked away with new knowledge! This rotation does have an on-call requirement, but it is more relaxed than other on call services. In my cohort, we were on call for 2 of the 14 days and would get a text if any patients were transferred to the service. If this did happen overnight, we would take over the case the following day and then be responsible for completing the patient's care.

The first week of the rotation was cut slightly short due to the Memorial Day holiday, but the rest of the days were packed full of wonderful educational opportunities. I had the opportunity to take part in multiple osteosarcoma cases which required full staging and a bone biopsy. In the world of oncology, almost everything revolves around the stage and grade of the tumor/cancer. Stage refers to how far the tumor has spread, while the grade refers to the morphology of the cells and how they appear under the microscope. These characteristics determine the potential treatment plans and can provide a projected estimate of the patient’s prognosis.

Here are some interesting tidbits about osteosarcoma:

Metastatic osteosarcoma is a tumor of the bone and accounts for 75-85% of primary bone tumors in dogs. 80% of cases occur in long bones (distal radius, proximal humerus, distal femur, and proximal tibia). There is a bimodal age distribution, so many patients may present between the ages of 1-2 or 7-9, but dogs can develop this cancer at any age. The prognosis for osteosarcoma is not great to say the least. If there is visible metastasis noted on radiographs, the median survival time is estimated to be about 2 months. 90% of cases have micrometastasis to the lungs at the time of diagnosis, which are not visible on radiographs. If an amputation is performed without the addition of chemotherapy, the median survival time is 4-6 months. If chemotherapy is added, that timeframe is extended to 9-12 months. If the owner elects stereotactic radiation therapy, the median survival time is 6-11 months, but this option should be considered carefully due to the high risk of a pathologic fracture. Palliative care can help keep the patient comfortable for a few weeks to months.

I also had the opportunity to work with a patient who had oral melanoma, and as a result, their mandible (lower jaw) was removed. This was done in an attempt to provide local tumor control and prolong the lifespan and quality of the patient. This patient is rechecked every 6 months to assess disease progression, and during these rechecks, thoracic rads and a neck ultrasound are performed. These imaging modalities screen for lymph node involvement or cancerous spread to other internal organs. Our little friend has not had any signs of disease progression in almost three years, which is unheard of for this type of cancer! A melanoma vaccine is also administered during these rechecks to extend the survival time in dogs with stage II or III oral melanoma once local disease control has been achieved.

With many cancer types, the host does not recognize cancerous cells as “foreign” so the immune system does not try to defend the body against the rogue cells. This form of tolerance can be overcome by vaccinating with an altered form of the antigen that is closely related to the original antigen. This may be derived from a different species (xenogeneic). The melanoma vaccine uses plasmid DNA that encodes the gene sequence from human tyrosinase, which is a protein expressed on the surface of human cutaneous melanocytes. Since there are significant differences between canine and human tyrosinase, the canine immune system recognizes the human form as “foreign”. These tyrosinases are similar enough that the immune response to the human form will cross-react with the canine form, leading to destruction of neoplastic melanocytes. Once the vaccine has been administered, the plasmid DNA is taken up by the host cells and then actively presented to the immune system.

Prior to the development of this vaccine, stage II and III oral melanoma had a median survival time of less than 5-6 months when treated with surgery alone. With the use of this vaccine, survival times have been seen to increase by about 10 months. While no treatment is perfect, this is a promising step in extending the lifespan of these patients with oral melanoma after local surgical excision. For more information on this product and further scientific studies, you can check out https://animalhealth.boehringeringelheim.com/pets/canine/products/therapeutics/oncept

This rotation also gave me the ability to learn about multiple chemotherapy agents and the rationale behind selecting an appropriate drug or drug combination. I was able to administer vincristine to a patient with a high-grade multicentric B-cell lymphoma (stage 5b). This drug inhibits mitotic spindle assembly, leading to mitotic arrest, and is specific to the metaphase portion of the cell cycle.

The second week of the rotation involved additional interesting cases, and I had the opportunity to observe a CT scan for the first time. This was performed with the intent of getting a better idea of tumor margins and location in a dog with a mass on the base of the heart and a separate mass extending from multiple lung lobes. While we had performed an ultrasound and thoracic rads earlier in the week, a CT scan was recommended so that we could assess if these tumors were resectable. Unfortunately, the tumor extension was more extensive than we had suspected with the radiographic views, and surgical removal is likely not a safe option.

This rotation also allowed me to explore some of the treatment options that our radiation oncology friends provide. Some tumors are not responsive to chemotherapy, so radiation therapy is sometimes elected to provide palliative care and help ease the discomfort associated with cancer.

Overall, this rotation was an incredible experience and gave me a new perspective on oncology. Unlike in humans, when chemotherapy is administered in companion animals, it is done at a much lower dose in an attempt to avoid a majority of adverse effects. Only about 20% of animals receiving chemotherapy experience adverse events, and out of those 20%, 5% will need to be hospitalized, and 1% may die. This is much different than in humans and is something that is important to explain to owners because, unlike in human medicine, we are not curing our patients with chemo; we are prolonging their quality of life.

I also had some amazing rotation mates and always felt supported by the team. Our last day included a Pokémon reveal, and we were all given a card that represented our personality.

Pokémon Reveal!

Quote of the rotation: “No dog should die without a little bit of pred.” – Dr. Gomez