Why is breast cancer considered so complex compared to other types of cancer, and what factors make it harder to find a universal cure?

 copy from Quora author Vitalsign for study and observation of cancer 

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Why is breast cancer considered so complex compared to other types of cancer, and what factors make it harder to find a universal cure?

The search for a breast cancer cure relies on a fundamental misconception. Breast cancer isn't a single disease,it’s dozens of distinct molecular illnesses merely sharing a location in the body.

This heterogeneity is the primary hurdle in finding a universal cure. Breast cancers are categorized by the receptors that drive their growth. Some tumors, fueled by hormones, are estrogen receptor-positive (ER+) or progesterone receptor-positive (PR+). Others overexpress a protein called HER2.

 And some, known as triple-negative, lack all three of these targets. 

A drug designed to block estrogen will starve an ER+ tumor but do absolutely nothing to a triple-negative cell.

Even within a single patient, a tumor is not a uniform mass of identical clones. As cancer cells divide, their genetic code becomes highly unstable, leading to rapid mutation. 

A tumor might start out with uniform characteristics but quickly evolve into a mosaic of genetically distinct cells.

A false-colored scanning electron micrograph of a breast tumor spheroid. The red regions indicate cells undergoing programmed cell death after exposure to an anti-cancer drug, while other layers of the spheroid continue to proliferate. Photo by Dr Khuloud T. Al-Jamal, via Europeana, is licensed under CC BY 4.0.

This internal diversity makes treatment a moving target. When a patient receives targeted therapy, the drug acts as an evolutionary pressure. It might wipe out most of the cancer cells, but any cells possessing a resistant mutation will survive and multiply. The tumor that eventually returns is biologically different and harder to treat than the one that was initially diagnosed.

The cancer's microenvironment adds another layer of complexity. 

Breast cancer cells constantly interact with surrounding connective tissue, blood vessels, and immune cells. Some tumors develop the ability to release signals that trick the immune system into ignoring them rather than attacking them.

When breast cancer metastasizes, it adapts to survive in entirely new ecosystems, such as the bones, liver, lungs, or brain. A breast cancer cell that thrives in the dense tissue of a liver requires entirely different survival mechanisms than one growing in the breast. Researchers treating metastatic patients are fighting cancer cells that have genetically rewired themselves to conquer a foreign organ.

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