Breast Cancer Takes on Many Forms, Some Common, Some Rare

Even though breast cancer mortality has been on the decline in recent years, it remains a leading cause of cancer deaths in women. This year an estimated 46,000 will die of the disease, and more than 180,000 women will be diagnosed.

But what is “breast cancer” anyway? Is it one disease or many? Myths and misleading notions are as pervasive about breast cancer as any other medical condition, doctors say. The truth is, breast cancer can manifest in many forms, some common, others rare.

And while all of the malignancies that invade the breast are called breast cancer, there are nuances in where and how these lesions occur and progress. Dr. Clifford Hudis, chief of the breast cancer service at Memorial Sloan-Kettering Cancer Center in Manhattan, said that in the most general of terms, the various forms of breast cancer derive their names from specific cell types.

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All tumors arise from cells that once were normal but undergo an irrevocable transformation. Some transform because of gene mutations. Other cells transform because of bombardment by hormones. For most cancers, the reason for the transformation will never be known.

Nevertheless, scientists do know that most breast cancers arise from epithelial cells, which line the body’s cavities. They form the secreting portions of glands and their ducts and are widespread throughout the body.

Carcinomas are the kinds of cancers that arise from epithelial tissue. Sarcomas, another group of cancers, arise from muscle tissue. For the most part, breast cancers are carcinomas because they occur in the epithelium.

Hudis believes that to better understand breast cancer, it is first necessary to understand the inner workings of the breast.

“In the normal breast, most of what you see physically is not breast tissue but fat and supporting tissue,” Hudis said. “From the nipple and branching out are the ducts. At the end of each of those little ducts are the lobules. Breast cancer is thought to arise at the ductal-lobular junction, right in the cells at the lobe and the duct.

“The naming of breast cancer comes from the appearance of the cells that the pathologist sees under a microscope,” Hudis said. “On the road to cancer there are a few things that can happen. The cells that line the ducts can grow in excess. This is what we call hyperplasia.”

Hyperplasia refers to an excessive proliferation of normal cells. Continuing on the road to cancer is a cellular condition known as atypical hyperplasia in which there is a distinct divergence from the normal cell type. These precancerous cells are a clue that a malignancy could occur at some point. Once cancerous cells take hold, they bear a distinct biological imprint. Cancerous cells replicate more rapidly than their healthy counterparts.

Additionally, there are molecular signatures, succinct and revealing, that typify cells born of a tumor. Some cancer cells are sensitive to estrogen and progesterone, two key female hormones. An estimated 25% to 30% of patients have the HER-2/neu gene, whose protein can make the cancer more likely to metastasize.

Some cells, though cancerous, are more like normal ones in their growth pattern and general appearance. Cancer cells that are the least like normal ones in growth and appearance are the most likely to be aggressive and put up a tougher fight.

These cellular and molecular nuances can be found in various forms of breast cancer.