What is acrometastasis?

Acrometastasis: Metastatic Cancer to the Extremities

Acrometastasis refers to metastatic cancer that has spread to the distal portions of the extremities, particularly the hands and feet, representing a rare but clinically significant manifestation of advanced malignancy with poor prognosis.

Definition and Epidemiology

Acrometastasis is an uncommon form of bone metastasis that affects the hands and feet, particularly the phalanges, metacarpals, and metatarsals. The incidence of acrometastases is extremely low, accounting for only about 0.1% of all bone metastases 1. This rarity makes them a challenging diagnostic entity that can be mistaken for other conditions.

Primary Cancer Sources

Acrometastases most commonly originate from:

• Lung cancer (most frequent)
• Kidney cancer
• Breast cancer
• Prostate cancer
• Colon cancer (less common)

The distribution pattern follows the general pattern of bone metastases, with lung cancer being the predominant source of acrometastases, followed by other common metastatic cancers 2.

Pathophysiology

The development of acrometastases follows the "seed and soil" concept of metastasis, where:

• Cancer cells ("seeds") from the primary tumor site enter the bloodstream
• These cells find favorable conditions ("soil") in the bone microenvironment
• The bone microenvironment provides growth factors that promote tumor cell proliferation
• The interaction between tumor cells and bone cells creates a "vicious cycle" that sustains metastatic growth 2

The relative rarity of acrometastases compared to other bone metastases may be related to:

• Reduced blood flow to the distal extremities
• Lower temperature in these areas
• Less red marrow in the small bones of hands and feet

Clinical Presentation

Patients with acrometastases typically present with:

• Pain and swelling in the affected digit or extremity
• Functional impairment
• Erythema and warmth that may mimic infection
• Pathological fractures
• In some cases, the acrometastasis may be the initial presentation of an occult malignancy 1

Diagnosis

The diagnostic approach includes:

1. Imaging studies:

   • Plain radiographs typically show lytic lesions, though some primaries (like prostate) may produce sclerotic lesions
   • MRI provides better soft tissue detail and extent of involvement
   • Bone scan can identify other sites of metastatic disease

2. Biopsy:

   • Essential for definitive diagnosis
   • Helps identify the primary tumor if unknown

3. Additional workup:

   • Comprehensive cancer staging with CT chest/abdomen/pelvis
   • Tumor markers based on suspected primary

Management

Treatment of acrometastases is primarily palliative, focusing on:

1. Pain control:

   • Analgesics following the WHO pain ladder
   • Radiation therapy for localized pain

2. Surgical intervention:

   • Amputation for intractable pain or fungating lesions
   • Stabilization of pathological fractures
   • Curettage and bone cement for selected cases

3. Systemic therapy:

   • Chemotherapy based on primary tumor
   • Targeted therapies when appropriate
   • Bone-modifying agents (bisphosphonates or denosumab) to reduce skeletal-related events 2

4. Radiation therapy:

   • Local radiation for pain control
   • May prevent pathological fractures

Prognosis

The presence of acrometastasis generally indicates advanced disease with poor prognosis:

• Median survival after diagnosis of acrometastasis is typically measured in months
• The appearance of acrometastasis often signifies widespread metastatic disease
• Treatment goals are primarily palliative rather than curative

Clinical Pearls and Pitfalls

• Acrometastases can be mistaken for infection, gout, or other inflammatory conditions
• The presence of acrometastasis should prompt a thorough search for the primary malignancy if not already known
• Biopsy is essential for definitive diagnosis
• Treatment should focus on palliation and quality of life
• The finding of acrometastasis should trigger discussions about goals of care and advanced care planning due to the poor prognosis

In summary, while rare, acrometastases represent an important manifestation of advanced malignancy that requires prompt recognition, appropriate diagnosis, and palliative management to improve quality of life in patients with limited life expectancy.