To help you advocate for your cat's health, we'll share our knowledge in a series of posts. The advocacy strategies discussed here concerning cancer apply to all cat health concerns. These posts won't be in any particular order, as their importance will depend on your specific situation. You can find the collection of tips here: Advocating for your cat: Helpful tips. Today's helpful tip: Cats, dogs, and humans are different.

One might easily assume that what's valid for humans and dogs is also valid for cats. I've repeatedly fallen into this trap in my frenzy to find research to help me make decisions about Ellie's care. Given the lack of research specific to cats with cancer, it's no wonder we want to assume the same things that apply to humans and dogs with cancer also apply to cats.

Unfortunately, the radiologist who did Ellie Mae's ultrasound communicated the prognosis for a dog with a 5-centimeter mass on her liver (likely not realizing the prognosis is different for dogs and cats). Primary liver tumors in dogs are more likely to be malignant than benign. And of those malignancies, the majority are hepatocellular carcinoma (HCC). In cats, primary liver tumors are more likely benign. The most common malignancy in cats with primary liver tumors is cholangiocarcinoma. Different chemotherapy drugs treat HCC than treat cholangiocarcinoma. And these two cancers usually carry vastly different prognoses. Our surgical resident said HCC doesn't usually grow back even when resection isn't complete. However, cholangiocarcinoma often later grows elsewhere in the liver, even when resection is complete.

Furthermore, chemotherapy agents used in humans and dogs may be toxic to cats. Unfortunately, cancer treatment research usually focuses on dogs and humans. So treatments available for dogs (and humans) that cats cannot tolerate leave a massive gap in treatment options for cats. 

Specifically, doctors often treat humans with cholangiocarcinoma with capecitabine or a combination of gemcitabine and cisplatin. Capecitabine and cisplatin are toxic to cats (but not dogs). Researchers don't understand why cats metabolize these drugs differently, but this severely impacts the effectiveness of treating cats with cancer. The lack of research on cat cancer treatment is a significant issue, as it means that the usual dire prognosis of cats with cholangiocarcinoma (6-month survival) will likely not change without more focused research.

However, people tend not to seek treatment for their cats' cancer, so without demand for these treatments, they will never happen. As cat lovers, you have the power to change this. By advocating for more research and treatment options for cats with cancer, you can help improve the prognosis for future cases. We've visited several oncology departments, wracking up over ten visits, and in all that time, we've only seen one other cat. All the case studies our oncologists quote are for dogs. But cats aren't little dogs.

Using the liver as an example, humans have four liver lobes. Dogs and cats have six. This difference in liver structure can significantly impact the surgical approaches used to remove liver masses. Often, doctors and veterinarians classify diseases differently. Veterinarians usually classify feline and canine cholangiocarcinoma as massive, nodular, or diffuse. In humans with cholangiocarcinoma, the disease is classified as intrahepatic (inside the liver), perihilar (in the hilum, which I can't put into layperson's terms), and distal cholangiocarcinoma (outside the liver). Please don't get caught up in the technical terms here. The overall point of this section is that what is true in humans or dogs doesn't always translate to cats; this is incredibly hard to accept. 

Why shouldn't it be the same? Despite my desire to answer this question for myself, I don't have the credentials or training to delve into this topic.

Note: This post is more technical than I would like. However, specific examples of the differences between cats, dogs, and humans were necessary to illustrate the point. We are not qualified to provide medical advice. If your cat or dog has a primary liver tumor, please seek the advice of an oncologist. Please also note that these issues are not specific to cholangiocarcinoma; the same problems apply to other cat cancers.