Sugar increases the Breast cancer

Christine Horner, reported high insulin levels are one of the biggest risk factors and promoters of breast cancer. Women with high insulin levels have a 283 percent greater risk of breast cancer.
Cancer cells love sugar. It's their preferred fuel. The more sugar you eat, the faster cancer cells grow. Our pancreas responds to sugar by releasing insulin, the hormone that escorts sugar into your cells. When we eat refined simple sugars, such as white table sugar, candy, cookies, or other sugar-laden foods, our blood sugar levels rise very quickly. Our pancreas responds by releasing a lot of insulin. That's not good

Eating sugar increases your risk of breast cancer:

It delivers a major blow to the immune system with the force of a prize fighter. Immune system is a natural defense against such invaders as bacteria, viruses and cancer cells. Research shows that right after you eat a high-sugar meal, your immune system function drops drastically. Sugar decreases T lymphocyte (a type of white blood cell), function by 50-94 percent. This effect lasts for a minimum of five hours. This means that right after you've eaten a lot of sugar our body's ability to fight off invaders or destroy cancer cells is tremendously weakened for several hours. 

Over a period of time, eating too much sugar can create imbalances that lead to two more deadly diseases: obesity and diabetes. Both of these diseases dangerously increase the risk of breast cancer. 

Insulin is consider unfriendly to breast cancer

When it comes to breast cancer, insulin is no friend. One of the biggest reasons is due to the fact that both normal breast cells and cancer cells have insulin receptors on them. When insulin attaches to its receptor, it has the same effect as when estrogen attaches to its receptor; it causes cells to start dividing. The higher the  insulin levels are, the faster the breast cells will divide; the faster they divide, the higher the risk of breast cancer is and the faster any existing cancer cells will grow. 
Insulin increases the estrogen levels i.e increase cell division:

As insulin levels are up, free-estrogen levels are up, and both of them speed up cell division.

There's also another detriment that high insulin levels can inflict. It makes more estrogen available to attach to the estrogen receptors in breast tissue. Insulin regulates how much of the estrogen in the blood is available to attach to estrogen receptors in the breast tissue. When estrogen travels in the blood, it either travels alone seeking an estrogen receptor, or it travels with a partner, a protein binder, that prevents it from attaching to an estrogen receptor. Insulin regulates the number of protein binders in the blood. So, the higher the insulin levels are, the fewer the number of protein binders there will be and therefore the more free estrogen that will be available to attach to estrogen receptors.