An Introduction to Breast Cancer

Improved screening has led to earlier detection of breast cancers, allowing more treatment options and decreased mortality rates.

A woman's lifetime risk of developing invasive breast cancer is approximately 1 in 8, or 12.5%.

Increasing age is the most significant risk factor for developing breast cancer apart from being female.

Having one first-degree relative with breast cancer doubles risk; having two or more increases risk five times. Familial and inherited mutations (e.g., BRCA1, BRCA2, p53) account for about 10% of cases.

Other important risk factors include early menarche, late menopause, nulliparity, late age at first live birth, prior breast biopsy, personal history of breast cancer, obesity (especially after menopause), alcohol consumption, use of hormone replacement therapy, and having dense breast tissue.

BRCA1 and BRCA2 mutations confer a 65-85% lifetime risk of breast cancer. BRCA1 also increases ovarian cancer risk (50%), and BRCA2 is associated with increased risks for ovarian, pancreatic, and male breast cancer.

Common signs and symptoms include abnormal mammogram findings, a painless firm mass, breast thickening or swelling, dimpling, nipple changes (ulceration, retraction, discharge), tenderness, skin irritation, and redness.

Most breast cancers develop at the terminal ductal lobular unit, with the upper outer quadrant (UOQ) being the most common site (38.5%).

Breast cancer is generally slow growing, taking about 5 years to become palpable. Disease can spread along ducts (carcinoma in situ), then invade surrounding tissues and spread via lymphatics, most often to axillary lymph nodes, and distantly to bone, lungs, liver, and brain.

Prognosis worsens with increased lymph node involvement. The more nodes involved and higher tumor grade, the greater the risk for metastasis and lower the survival rate.

The primary types are ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS), invasive ductal carcinoma (IDC), invasive lobular carcinoma (ILC), inflammatory carcinoma, and others (e.g., medullary, mucinous, tubular).

Hormone receptor-positive breast cancers (ER+ and/or PR+) respond to hormone therapies and have a better prognosis than receptor-negative cancers.

HER-2/neu is a growth-promoting protein overexpressed in up to 30% of breast cancers, associated with aggressive tumors and decreased disease-free survival. HER-2 positive cancers benefit from targeted therapies like trastuzumab (Herceptin) and lapatinib (Tykerb).

Women at average risk should start annual mammogram screening and annual clinical breast exam at age 40.

Moderate risk women (15-20% lifetime risk) may consider adding MRI to mammogram annual screening from age 40. High-risk women (>20% lifetime risk, BRCA mutation, or relevant family/genetic history) should start annual mammogram and MRI at age 30, plus annual clinical breast exam.

Screening mammograms detect cancer in about 3 out of every 1,000 women screened (0.3%).

The sensitivity of mammography is approximately 90% and specificity is about 94%, but both can vary (sensitivity 60-95%, specificity 50-98%).

Mammography has reduced sensitivity in dense breasts, may fail to detect small lesions or some types like invasive lobular carcinoma, and does not reliably assess disease extent.

Breast MRI detects otherwise occult contralateral breast cancer in about 3-4% of women with newly diagnosed breast carcinoma.

Indications include screening in moderate/high risk women, evaluation of dense breasts, monitoring neoadjuvant therapy response, assessing extent of disease in those with personal breast cancer history, and surgical planning (breast conservation vs. mastectomy).

MRI has higher sensitivity (77-100% vs. 16-40% for mammography) but slightly lower specificity (81-99% vs. 93-99%). MRI is more effective in high-risk groups and dense breasts.

Improved screening has led to earlier detection of breast cancers, allowing more treatment options and decreased mortality rates.

A woman's lifetime risk of developing invasive breast cancer is approximately 1 in 8, or 12.5%.