Does a 6 cm humerus (upper arm bone) enchondroma (type of benign bone tumor) warrant a biopsy (tissue sample examination)?

Management of a 6 cm Humerus Enchondroma: Biopsy is Warranted

A 6 cm enchondroma in the humerus warrants biopsy due to its large size and location in a long bone, which increases the risk of malignant transformation. 1

Risk Assessment for Enchondromas

Enchondromas are benign cartilaginous tumors that typically occur in the metaphyseal region of long bones. While most enchondromas are benign and can be managed conservatively, certain features raise concern for potential malignancy:

High-Risk Features:

• Size > 5-6 cm (present in this case)
• Location in long bones (humerus is a high-risk location)
• Pain at the site (if present)
• Cortical destruction or soft tissue extension

Diagnostic Algorithm

1. Initial Imaging Assessment

   • Conventional radiographs in two planes should be the first investigation
   • MRI of the entire compartment with adjacent joints for local staging 2
   • Contrast-enhanced MRI can reveal high-grade areas that may guide biopsy 2

2. Decision for Biopsy

   • For enchondromas > 5-6 cm (as in this case), biopsy is recommended 1
   • The American Academy of Orthopaedic Surgeons recommends dedicated MRI for lesions >5-6 cm or in high-risk locations like the humerus 1

3. Biopsy Procedure

   • Should be performed at a bone sarcoma reference center 2
   • Core-needle biopsy under imaging control is often appropriate 2
   • The biopsy should be performed by the surgeon who will carry out any potential definitive tumor resection 2

Rationale for Biopsy in This Case

The differentiation between benign enchondroma and low-grade chondrosarcoma can be difficult based on imaging alone 2. While enchondromas in the phalanges of hands and feet rarely undergo malignant transformation, central cartilaginous lesions in other long bones like the humerus should be considered potential low-grade chondrosarcomas until proven otherwise 2.

The 6 cm size of this enchondroma is particularly concerning, as the National Comprehensive Cancer Network and American Academy of Orthopaedic Surgeons specifically recommend additional evaluation for lesions >5-6 cm 1.

Management Following Biopsy

Based on histological findings, management options include:

• If confirmed benign enchondroma:

  • Surveillance with physical examination and imaging every 6-12 months for 2 years, then yearly 1
  • Consider curettage with or without bone grafting if symptomatic 3

• If low-grade chondrosarcoma:

  • Grade I chondrosarcomas in long bones can be managed by curettage with adjuvant treatment (phenol, cement, cryotherapy) 2
  • Higher-grade chondrosarcomas require wide surgical excision 2

Important Caveats

• Histological grading of cartilaginous tumors can be challenging with significant inter-observer variability, even among experts 2
• Enchondroma growth is relatively rare (5.45% in one study) but typically occurs around two years of follow-up 3
• Unnecessary surveillance of definitively benign lesions can lead to significant patient costs without clear oncologic benefit 3
• Pain at the site of a cartilaginous lesion may indicate malignant transformation and should prompt immediate evaluation 2, 1

The large size (6 cm) of this humerus enchondroma, combined with its location in a high-risk bone, makes biopsy necessary to rule out malignant transformation and guide appropriate management.