Understanding the Types of Paget's Disease
To understand what secondary Paget's disease is, it is crucial to first distinguish it from the more well-known, non-malignant form. The term 'Paget's disease' can refer to several different conditions, primarily Paget's disease of bone and mammary or extramammary Paget's disease of the skin. The distinction between primary and secondary types is based on the origin of the malignant cells.
Secondary Paget's disease is not a condition that arises spontaneously but is a symptom of an underlying, more aggressive cancer. In contrast, primary Paget's disease of bone is a metabolic disorder causing abnormal bone remodeling, and primary cutaneous Paget's is an intraepithelial skin malignancy that starts in the skin itself. The 'secondary' classification points to a much more ominous prognosis due to the underlying visceral malignancy.
Secondary Extramammary Paget Disease (EMPD)
Secondary EMPD occurs when malignant cells from an internal cancer spread to the epidermis, most commonly in the genital or perianal regions. The cancer cells travel from their origin, often the gastrointestinal (GI) or genitourinary (GU) tract, to the skin. Cancers commonly associated with secondary EMPD include:
- Colorectal carcinoma
- Urothelial carcinoma (bladder or urethral cancer)
- Prostatic, cervical, or ovarian carcinoma
- Anal gland carcinoma
Histopathologically, distinguishing between primary and secondary EMPD is critical for determining the correct treatment strategy and assessing prognosis, which is generally much poorer for secondary forms.
Secondary Cancer Arising from Paget's Disease of Bone
While Paget's disease of bone is not a cancer, a rare but serious complication is its malignant transformation into a form of bone cancer, most commonly osteosarcoma. This is sometimes referred to as 'pagetic sarcoma.' The risk of this transformation is low (0.15% to 1%) but significantly increases in patients with long-standing, polyostotic (multiple bone) disease.
This secondary osteosarcoma typically occurs in the weight-bearing bones and skull, reflecting the areas most commonly affected by the underlying Paget's disease of bone. The prognosis for this type of secondary cancer is poor, even with aggressive treatment.
Symptoms and Diagnosis
Because secondary Paget's is a manifestation of another cancer, the symptoms are influenced by both the underlying malignancy and the affected tissue. The cutaneous form, EMPD, often presents with a rash that is red, scaly, or crusty, and can be itchy, mimicking common skin conditions like eczema. In the case of sarcomatous transformation of Paget's of bone, symptoms include severe and persistent bone pain, swelling, or the appearance of a new soft-tissue mass.
Diagnosis involves a detailed patient history and thorough examination, followed by tissue biopsies and further investigations. The use of immunohistochemical markers is often necessary to determine whether the cells originated from the skin or an internal organ.
Comparison of Primary vs. Secondary Paget's
| Feature | Primary Paget's (EMPD or Bone) | Secondary Paget's (EMPD or Sarcoma) |
|---|---|---|
| Origin | Arises from local cells (epidermis, apocrine glands, or bone). | Caused by the spread of an underlying visceral cancer to the skin or bone. |
| Associated Malignancy | Not associated with internal or systemic cancer. | Directly caused by an underlying internal malignancy, most often from the GI or GU tract. |
| Prognosis | Generally good if confined to the skin or manageable in the case of bone disease. | Poor due to the nature of the underlying visceral cancer. |
| Treatment | Focused on the local disease, often involving surgical excision or topical treatments for EMPD; bisphosphonates for bone disease. | Requires treatment of both the local manifestation and the underlying systemic cancer. |
| Metastasis | Primary EMPD can metastasize if left untreated, but secondary is already a metastatic process. | The condition itself is a form of metastasis, and systemic spread is often more advanced. |
| Demographics | Varies by type (e.g., bone disease more common in older men of European descent). | Associated with older age and presence of pre-existing conditions. |
Management and Outcome
Management of secondary Paget's disease is significantly more complex than treating primary forms and requires a multidisciplinary approach involving oncologists, surgeons, and dermatologists. The strategy is dictated by the type and extent of the underlying cancer.
- Secondary EMPD: Treatment involves addressing the underlying visceral carcinoma, which is the primary cause of the skin lesion. Surgical removal of the skin lesion is often part of a broader treatment plan that may include chemotherapy or radiation for the internal cancer.
- Pagetic Sarcoma: The prognosis is very poor, and aggressive treatment is typically required, including surgery and combination chemotherapy. Despite this, survival rates are often low.
The prognosis for secondary Paget's is heavily dependent on the stage and resectability of the underlying malignancy. Early detection and treatment of the primary cancer are critical for improving outcomes. However, the diagnosis of secondary Paget's often indicates a more advanced stage of disease.
Conclusion
In conclusion, secondary Paget's disease is a serious condition representing the spread of an aggressive internal cancer to either the skin (Extramammary Paget Disease) or bone (osteosarcoma). This is a distinctly different and more serious diagnosis than the primary, non-cancerous Paget's disease of bone or the less aggressive primary cutaneous EMPD. Diagnosis requires careful pathology and screening for underlying malignancy, and treatment focuses on the systemic cancer. The prognosis for secondary Paget's disease is less favorable than for its primary counterparts due to its malignant, metastatic nature. A comprehensive understanding of the origin of the cancerous cells is essential for effective management and prognostication.
For more information, see the National Organization for Rare Disorders (NORD) page on Paget's disease.
