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Though breast cancer is one of the most common types of cancer among women, its exact cause and mechanism are not yet fully understood. Now, scientists at the University of Michigan Comprehensive Cancer Center said they found a key genetic diver for a rare form of breast cancer.

For more than 10 years, scientists have been studying how a poorly understood protein called CCN6 affects breast cancer. They examined the effects of CCN6 deletion from the mammary glands in mice. Results of the experiment show delayed development and mammary glands did not develop properly at different ages.

One year after, the laboratory mice formed mammary gland tumors, which looked the same as human metaplastic breast cancer. This type of cancer is very rare and aggressive subtype of triple-negative breast cancer, which accounts for 20 percent of all breast cancers. Moreover, about only 1 percent is metaplastic breast cancer.

It differs from the more common types of breast cancer in both its makeup and in its behavior. Usually, this type of cancer begins in the milk duct of the breast before spreading to the tissue around the duct. One of the unique characteristics of a metaplastic tumor is the kind of cells it has, which appear abnormal when seen under a microscope. The cells look like the soft tissue and connective tissue in the breast, which is thought to have undergone a change in form to become completely different cells.

With its uniqueness and complexity, metaplastic breast cancer is very hard to treat, or even diagnose.

"Metaplastic breast cancers are challenging to diagnose and treat. In part, the difficulties stem from the lack of mouse models to study this disease," Dr. Celina Kleer, director of the Breast Pathology Program at the University of Michigan Comprehensive Cancer Center, said in a press release.

"Our hypothesis, based on years of experiments in our lab, was that knocking out this gene would induce breast cancer. But we didn't know if knocking out CCN6 would be enough to unleash tumors, and if so, when, or what kind. Now we have a new mouse model, and a new way of studying metaplastic carcinomas, for which there's no other model," she added.

The scientists also found that metaplastic cancer cells are mesenchymal, which move and invade. They found that deleting the CCN6 in their mouse model induced the process called epithelial to mesenchymal transition.

The researchers did not only gain a better understanding of CCN6 but also, they opened the door to a better understanding of the rare disease and possibly, a new way to treat it. The team plans to test potential therapies and therapeutics in combination with existing treatment options to gain a better understanding of the disease and discover new genes that play a role in the disease's development.

The study was published in the journal Oncogene.