Introduction 

Breast cancer is a disease in which malignant (cancerous) cells form in the tissues of the breast. It is one of the most common cancers in women, accounting for around 30% of all new cancer diagnoses. According to the American Cancer Society, around 287,000 new cases of invasive breast cancer will be diagnosed in women in the United States this year. 

While breast cancer also occurs in men, it is about 100 times more common in women. The good news is that thanks to earlier detection and improved treatments, survival rates continue to improve. The 5-year relative survival rate for stage 0 or 1 breast cancer is close to 100%, while for stage 4 breast cancer it is around 22%. This highlights the importance of early detection through screening and increased awareness of symptoms. The earlier breast cancer is found, the more likely treatment will be successful.

Types of Breast Cancer

Breast cancer is categorized into different types based on certain characteristics of the cancer cells. The main types of breast cancer are:

Invasive vs Noninvasive 

• Invasive breast cancers - These breast cancers have spread into surrounding breast tissue. The most common invasive breast cancers are invasive ductal carcinoma and invasive lobular carcinoma.
• Noninvasive breast cancers - These breast cancers are confined to the ducts or lobules of the breast and have not spread to surrounding tissue. The most common types are ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS).

Hormone Receptor Status

Breast cancer cells may or may not have receptors for the hormones estrogen and progesterone. These receptors determine how the cancer cells grow and spread.

• Hormone receptor positive - The cancer cells have estrogen receptors (ER+) and/or progesterone receptors (PR+). These cancers can be treated with hormone therapy.
• Hormone receptor negative - The cancer cells lack estrogen and progesterone receptors (ER- PR-). These cancers do not respond to hormone therapy.

HER2 Status 

HER2 is a protein that promotes cancer cell growth.

• HER2 positive - The cancer cells have higher than normal levels of the HER2 protein. These cancers tend to be more aggressive but respond well to HER2 targeted therapy.
• HER2 negative - The cancer cells have normal levels of HER2 protein.

Knowing the type of breast cancer helps determine the most effective treatment options.

Risk Factors

There are several factors that are known to increase a woman's risk of developing breast cancer:

Age

The risk of breast cancer increases as a woman gets older. Most breast cancers are diagnosed after age 50.

Family History

Women with close blood relatives who've had breast cancer have a higher risk. Having a first-degree relative (mother, sister, daughter) diagnosed increases risk 2-3 fold.

Genetic Mutations 

About 5-10% of breast cancers are thought to be hereditary, caused by gene mutations passed down in families. The BRCA1 and BRCA2 genes are responsible for most inherited breast cancers. Women with these mutations have a 50-85% lifetime risk.

Lifestyle Factors

There are some lifestyle factors that are linked to higher breast cancer risk like drinking alcohol, being overweight or obese after menopause, physical inactivity, and using combination hormone therapy after menopause. However, many studies have shown these only increase risk slightly.

The most significant risks for breast cancer are being female and growing older. It's important for all women to discuss their personal risk factors with their doctor to determine when to begin screening.

Early Detection

Detecting breast cancer at the earliest possible stage offers the greatest chance for successful treatment. There are a few ways that women can watch for early signs of breast cancer.

Self Exams

Doing regular self-breast exams is important for getting familiar with how your breasts normally look and feel. This can help you notice any changes early. Experts recommend doing self-exams at least once a month. The best time is several days after your period ends, when breasts are less likely to be swollen or tender. Observe your breasts in the mirror for any changes in shape or appearance. Use a pattern to examine every section of your breast, including the underarm and collarbone areas. Feel for any lumps, thickening, or changes in skin texture. Report any noticeable changes to your doctor right away.

Clinical Exams  

During your regular health check-ups, your doctor will perform a clinical breast exam. They will carefully feel for any lumps or abnormalities. Women in their 20s and 30s should have a clinical breast exam as part of their exam every 1-3 years. After age 40, it is recommended annually.

Mammograms

A mammogram is an x-ray of the breast. It can detect tumors that are too small to feel. Mammography is the only screening tool proven to reduce breast cancer deaths. The U.S. Preventive Services Task Force recommends women at average risk start yearly mammograms at age 50 and continue until age 74. Those at high risk may need to start earlier. Always follow your doctor's recommendations on when and how often to get a mammogram.

Other Imaging Tests

If a lump is detected through self-exam or mammogram, your doctor may order further imaging tests. An ultrasound uses sound waves to examine breast tissue in real time. It can differentiate between fluid-filled cysts and solid masses. An MRI involves radio waves and strong magnets to create detailed cross-sectional images. Though not used for routine screening, an MRI can provide additional information if results are unclear. Discuss with your doctor which tests are appropriate for your individual situation.

Diagnosis

Once breast cancer is suspected, the next step is a thorough evaluation to determine the characteristics of the cancer, whether it has spread, and what the best treatment options are. There are several components involved in the breast cancer diagnosis process:

Biopsy

A biopsy is the only definitive way to diagnose breast cancer. This procedure removes a small amount of tissue from the suspicious area so it can be examined under a microscope. There are a few types of biopsies:

• Core needle biopsy: A hollow needle is inserted into the breast lump to extract a sample of cells and tissue. This is usually performed under local anesthesia.
• Surgical biopsy: The entire lump or suspicious area is removed during a minor surgical procedure under local or general anesthesia. Several types of surgical biopsies can be performed, such as lumpectomy, incisional biopsy, or excisional biopsy.
• Vacuum-assisted biopsy: Uses imaging guidance to insert a hollow probe into the breast lump and suction out tissue samples. Only requires a small incision.

A breast biopsy provides the cells and tissue needed to establish an accurate diagnosis. A pathologist will analyze the biopsy sample(s) and write up a pathology report detailing the findings.

Pathology Report 

The pathology report contains important information about the characteristics of the breast cancer that will guide treatment decisions. Details included in the pathology report:

• Cancer type (invasive vs in situ)
• Grade (how abnormal the cells look; lower grade = slower growing) 
• Estrogen/progesterone receptor status 
• HER2 status 
• Margins status (clean vs cancer cells at edge)
• Lymph node evaluation 

These factors indicate how aggressive the cancer is and which targeted therapies may be effective.