Canine mammary cancer study explores new techniques for early detection

Canine mammary cancer is the most common type of cancer found in unspayed female dogs, accounting for 40 per cent of diagnosed tumours. More than 25 per cent of these dogs will develop a mammary tumour in their lifetime, a significant health threat that only increases with age.

“Unfortunately, with canine mammary cancer, there aren’t options for early intervention,” explains Dr. Melissa Meachem (DVM'08, MVetSc'13), an assistant professor in the WCVM’s Department of Veterinary Pathology. “Because of this, about 50 per cent of canine mammary tumour cases we see are malignant by the time they are detected by caregivers. They’ve likely grown and spread to other parts of the body, reducing successful treatment options like surgery.”

In 2022, Meachem received US$30,000 to begin a research project that explores opportunities for early canine mammary cancer intervention by studying the cancer’s interactions with the body’s immune system. The research grant came from Morris Animal Foundation (MAF), an American non-profit organization that supports innovative veterinary research for companion animals, horses and wildlife.

Pet Valu and Blue Buffalo Co., Ltd., pet supply retailers in Canada and the United States, are funding partners on the project.

“It’s a highly competitive grant,” says Meachem, adding that the MAF application process was rigorous and required detailed planning. After her application went through the initial rounds of scientific review, there were “multiple instances where we discussed with their scientific advisers the protocols that we were planning on taking.

“I’m really grateful for their support — it’s been really fundamental for making this project happen.”

Meachem is investigating the potential of the cancer expressing certain proteins in development that mask the tumour’s presence from immune system detection, allowing it to grow and spread unchecked.

“It’s a fascinating process that’s occurred in human breast cancer studies, but it hasn’t been explored thoroughly in canine mammary cancer,” she says.

“We’re looking at whether benign tumours and malignant tumors are both expressing three specific proteins — programmed death-ligand 1 (PD-L1), programmed cell death protein 1 (PD-1), and T cell immunoglobulin and ITIM domain (TIGIT) — that are known to occur in human breast cancer studies,” says Meachem.

“If this process is occurring, we want to know whether it’s actually occurring earlier in the pre-cancerous lesions that we can see in the canine mammary tissue.”

This analysis involved gathering data from over 500 archived biopsy samples of mammary tissue from diagnostic cases through Prairie Diagnostic Services (PDS), the provincial veterinary diagnostic laboratory in Saskatchewan.  

“I was tasked with sorting through these cases and separating data into fine criteria and getting an understanding of each dog’s history, and age and any further conditions,” says Dr. Shanika Kurukulasuriya (BVSc, PhD'17). The graduate student worked on the project as part of her Master of Veterinary Science (MVetSc) degree in clinical pathology.

“We needed to narrow the cases to the find the ones that best represented what we were looking for.”

Meachem and Kurukulasuriya then tested the samples using immunohistochemistry — the process of producing a special stain that binds to specific proteins based on a selected antibody. This technique allows researchers to evaluate the amount of staining in correlation to how much of the protein is being expressed. They can further examine where the protein is being expressed in the cells and how many cells express it.

“We analyzed the staining manually through microscopes, but in this case, we also trained a computer program called QuPath to semi-automatically score our data,” says Meachem.

The program digitally scans the slides and is scripted to differentiate and display unique data sets between tumour cells, saving time and avoiding potential errors related to human analysis. QuPath also allows researchers to view an entire tumour instead of small samples, offering a major advantage in gathering consistent information.

“We can ask the program ‘How many cells are showing positive markers?’ or ‘How many cells are showing as a different colour?’ It’s pretty neat because instead of the subjectivity of a person looking at the data, this program is very objective,” says Meachem.

The WCVM researchers are now analyzing the collected data before publishing their findings, which have revealed some unexpected results.

“Our initial results suggested that canine mammary cancer doesn’t quite follow the pattern we expected to see when compared to research literature in human breast cancer,” says Meachem.

The WCVM researchers found that the average expression of PD-L1 was lower in the malignant mammary tumour group, which is contrary to previously published findings on canine and human mammary cancer.

“We found that our pre-cancerous cells express a lot of PD-L1. This is something that hasn’t really been reported before, but it does seem like this protein plays a really important role in cell growth and survival.”

Meachem is intrigued by this concept. She wants to follow up with future research efforts — particularly exploring how this protein expression could be used as an early marker in developing diagnostic tools for earlier detection of mammary cancer.

“I feel very optimistic with our findings. Some of the proteins we studied may not be as useful in early detection, but I’m hopeful that the protein we found differentially expressed could prove useful through future research.”

Article originally published at https://wcvmtoday.usask.ca