Paget’s disease of the breast (PDB) is a rare form of cancer that begins in the milk ducts and extends to the skin of the nipple and areola, affecting only about one to four percent of all breast cancer patients. The progression of PDB is highly variable and depends almost entirely on the nature of the underlying tumor within the breast. The visible changes on the nipple skin often progress slowly over many months. This slow progression can lead to a delayed diagnosis, as symptoms are frequently mistaken for a common skin condition.
Defining Paget’s Disease and Initial Presentation
Paget’s disease of the breast manifests externally with symptoms that mimic benign skin disorders such as eczema or dermatitis. The primary physical signs appear on the nipple and sometimes the surrounding areola, typically affecting only one breast. Early symptoms commonly involve redness, flaking, or a scaling rash on the nipple skin, often accompanied by persistent itching, tingling, or a burning sensation. As the condition progresses, the skin may become thickened, crusted, or ulcerated, sometimes leading to a yellowish or bloody nipple discharge. Over time, the nipple itself may become flattened or retracted, and these superficial changes progress gradually over a period of months or even years, often leading to misdiagnosis and a significant delay before a definitive cancer diagnosis.
The Crucial Link to Underlying Cancer
PDB is a manifestation of an underlying cancer within the breast in the vast majority of cases, ranging from 85 to 95 percent of diagnoses. The accepted theory is that malignant cells, known as Paget cells, originate from a tumor deeper inside the breast and travel up the milk ducts to the nipple surface. The rate of disease progression is therefore directly tied to the biological behavior of this associated tumor, not the visible skin changes. The underlying cancer is typically categorized into two main types: Ductal Carcinoma In Situ (DCIS) or Invasive Ductal Carcinoma (IDC). DCIS is considered a non-invasive, or “stage 0,” cancer where the cells are confined to the milk ducts and have not spread into the surrounding breast tissue.
When PDB is associated only with DCIS, the progression risk is much slower because the cancer cells are contained. However, in roughly 30 to 50 percent of PDB cases, an invasive cancer is also present, which is a far more serious condition. IDC means the malignant cells have broken through the duct walls and entered the fatty tissue of the breast. This type of underlying tumor carries a much higher and faster risk of systemic progression, meaning the cancer cells can potentially travel to other parts of the body through the bloodstream or lymphatic system.
Factors That Determine Progression Speed
The most significant factor influencing the speed is whether the underlying tumor is non-invasive (DCIS) or invasive (IDC) at the time of diagnosis. If the disease is confined to DCIS, the progression is inherently slower as the cancer is biologically non-invasive and contained. The presence of a palpable lump in the breast, in addition to the nipple changes, is a strong indicator of a more advanced, and thus faster-progressing, disease. About half of patients with PDB have such a lump, which is often a sign of an underlying invasive tumor with a higher risk of spread.
When an invasive tumor is present, the speed of progression is then determined by additional microscopic factors. One such factor is the tumor grade, which describes how aggressive the cancer cells look under a microscope. Higher-grade tumors have cells that divide more rapidly and look less like normal cells, indicating a faster pace of growth and a higher potential for spread.
The presence of cancer cells in the lymph nodes outside the breast is another major determinant of progression speed, signaling that the disease has already become systemic. Furthermore, the molecular profile of the tumor plays a role, as a high percentage of PDB cases are positive for the HER2 protein, which is often associated with a more aggressive form of breast cancer.
Diagnostic Timeline and Staging
The first definitive step is a biopsy of the nipple skin, which confirms the presence of Paget cells and establishes the diagnosis of PDB. Following this confirmation, the focus immediately shifts to determining the extent of the underlying cancer, which dictates treatment urgency. A comprehensive imaging workup is essential, typically including a diagnostic mammogram, breast ultrasound, and often a Magnetic Resonance Imaging (MRI) scan. These tests search for any mass or abnormal area deeper within the breast tissue, and if found, a core needle biopsy is performed to confirm the type of cancer and its characteristics. The progression of the disease is determined by the TNM (Tumor, Node, Metastasis) staging system, just like any other breast cancer, with PDB itself classified as Tis (Paget) if no other cancer is found.