Paget’s disease of the breast is a rare type of breast cancer that primarily affects the nipple and the surrounding areolar skin. The exact cause of Paget’s disease of the breast is not fully understood, but the most widely accepted explanation involves the presence of an underlying breast cancer, usually ductal carcinoma, that spreads to the nipple area.
In this condition, cancer cells originate deeper within the breast ducts and then migrate through the milk ducts toward the nipple. These malignant cells infiltrate the epidermis—the outer layer of skin on the nipple and areola—causing visible changes such as redness, scaling, crusting, and sometimes oozing or thickening of the skin. This process leads to symptoms that often resemble eczema or dermatitis but do not improve with typical skin treatments.
There are two main theories about how Paget’s disease develops:
1. **Migration Theory:** This is the most accepted theory. It suggests that cancer cells from an underlying ductal carcinoma in situ (DCIS) or invasive breast cancer travel through the lactiferous ducts to the nipple skin. These cells then proliferate in the epidermis, causing the characteristic skin changes. This explains why Paget’s disease is often associated with a deeper breast tumor, which may or may not be palpable or visible on imaging.
2. **In Situ Transformation Theory:** A less common theory proposes that the malignant cells arise independently within the nipple epidermis itself, without an underlying breast tumor. This would mean the cancer starts directly in the nipple skin rather than spreading from deeper breast tissue.
Paget’s disease typically affects women in their 50s and 60s but can occur at other ages. It accounts for about 1-5% of all breast cancers. The disease often begins with symptoms such as itching, burning, or tenderness of the nipple, followed by visible changes like redness, flaking, or crust formation. Over time, the lesion may enlarge, crack, and ooze, resembling a persistent eczema that does not respond to standard treatments.
Histologically, the disease is characterized by the presence of large, malignant epithelial cells known as Paget cells within the epidermis. These cells disrupt the normal skin structure and cause inflammation and irritation. Several variants of Paget cells exist, including adenocarcinoma-like, spindle cell, anaplastic, acantholytic, and pigmented types, reflecting the diversity in cellular appearance under the microscope.
Risk factors for developing Paget’s disease of the breast largely overlap with those for breast cancer in general. These include increasing age, genetic predispositions such as BRCA gene mutations, family history of breast cancer, hormonal factors like late menopause or having a first child at an older age, and lifestyle factors including obesity, alcohol consumption, and smoking. Both women and men can develop Paget’s disease, though it is far more common in women.
Because Paget’s disease is often linked to underlying breast cancer, it is important to evaluate the entire breast carefully when symptoms appear. Diagnosis typically involves a clinical examination, imaging studies such as mammography or MRI, and a biopsy of the nipple skin to identify Paget cells. Early detection is crucial because treatment usually involves surgery to remove the affected tissue, often combined with other therapies depending on the presence and extent of underlying cancer.
In summary, Paget’s disease of the breast is caused by malignant cells spreading from an underlying breast cancer to the nipple skin or, less commonly, arising directly in the nipple epidermis. This leads to characteristic skin changes and symptoms that signal the presence of a serious breast condition requiring prompt medical attention.
