The tissue obtained from a core needle or open surgical biopsy is sent to a pathologist for evaluation. The pathologist then generates a report documenting his or her findings. For a patient diagnosed with breast cancer, this pathology report contains many important details about her breast cancer, including the type of breast cancer, the grade of the breast cancer, and the receptor status of the breast cancer.

Type

The type of cancer typically will be listed first. Cancer that extends into the breast tissue is called invasive breast cancer. Invasive cancer can break away from the breast and spread. The most common type of invasive breast cancer is infiltrating ductal carcinoma, also called ductal carcinoma. Ductal carcinoma originates in the ducts of the breast. Subtypes of invasive ductal carcinoma are named with descriptive terms, such as mucinous colloid carcinoma (mucin-producing cancer) and papillary carcinoma (cancer arising from a growth within a specific duct).

Among the other forms of invasive breast cancer is lobular carcinoma, which starts in the milk-producing portion of the breast (the lobules of the breast). Rare types of invasive carcinoma include inflammatory breast cancer (a cancer which invades the lymphatic system under the skin and creates an orange skin appearance called peau d’orange), Paget’s disease (a skin manifestation of an underlying breast cancer), primary lymphoma of the breast, and cancers that have spread to the breast from other organs (metastatic cancer), such as melanoma.

Pre-invasive breast cancer is contained within the ducts and does not spread (metastasize). Nevertheless some pre-invasive breast cancers can turn into invasive breast cancers. Because of this malignant potential, pre-invasive breast cancer can be a problem for individual patients. The most common type of pre-invasive breast cancer is ductal carcinoma in-situ, or DCIS. Lobular carcinoma in-situ (also called LCIS) and papillary carcinoma in-situ are the next most frequently noted pre-invasive breast cancers.

Grade

The grade of breast cancer is often mentioned in the pathology report after the type of breast cancer. The grade is determined by what the pathologist sees when looking at the breast cancer under the microscope. The pathologist looks for how many cells are dividing (mitoses), the architecture of the breast tissue (tubules), and how the individual cells appear (atypia). Each of these components (mitoses, tubules, and atypia) is given an individual score of 1, 2, or 3. These 3 scores are added together to determine the overall grade of the cancer. A grade 1 cancer has more favorable biology and is often called a low-grade cancer. A grade 2 cancer is considered intermediate grade and a grade 3 cancer is referred to as a high-grade cancer.

Receptor Status

The breast cancer cell’s surface has receptors that serve to regulate the cell’s functions. These receptors are comparable to locks. The keys that fit into these locks will “turn on the engines” of the breast cancer cell and stimulate growth. The 3 breast cancer cell receptors in invasive breast cancers that are most commonly checked by the pathologist are the estrogen receptors, the progesterone receptors, and the HER2 receptors. For pre-invasive breast cancers, typically the estrogen and progesterone receptors are tested, but not the HER2 receptors.

If the breast cancer cell has a specific receptor on its surface, the specific receptor is called positive. If the breast cancer cell does not have that specific receptor on its surface, the specific receptor is called negative. This information is very important as it helps a doctor offer therapy that will benefit a patient and avoid prescribing treatment that does not work on an individual breast cancer.

For example, if the estrogen receptor is positive, then that breast cancer cell’s surface contains the lock for estrogen and that patient would benefit from a medicine that competes with the natural key of estrogen, such as tamoxifen. For breast cancers that test positive for HER2 receptors, the medications that fit into the HER2 receptor are very effective. For breast cancers with negative receptors, the addition of receptor-targeted drugs will not help the patient and will add all the unwanted side effects of that receptor-targeted drug. Therefore a different class of medications will be required to treat these negative receptor breast cancers.

Often the pathology report includes a numerical value next to the receptor’s positive or negative value. The more receptors found on the surface of the breast cancer cell, the higher the number. For example, an estrogen receptor with the value of 100 will be very sensitive to estrogen stimulation and in that case drugs that compete with estrogen will greatly benefit the patient. While the numerical value assigned to a negative result is usually 0, some reports may assign a numerical number to a negative result. This can be clarified by the patient’s physician. Note that some reports may use the term “strongly positive” or “weakly positive” rather than assign a numerical value.

While the pathologist provides a variety of descriptive details in the report, the most important for patients and doctors alike are type, grade, and receptor status.

It is important to note that the size of the tumor stated in a core needle biopsy does not reflect the actual size of the breast cancer, except for the cases where a very small breast cancer is removed during the process of the core needle biopsy. The purpose of the core needle biopsy is to provide the pathologist with enough tissue to diagnose a breast cancer.