DNA Index Assessment in Neuroblastoma
DNA index (ploidy status) is assessed using flow cytometry, which measures the amount of DNA within tumor cells to determine if they are diploid (DNA index = 1) or aneuploid (DNA index > 1). 1
Primary Method: Flow Cytometry
Flow cytometry is the established technique for determining DNA ploidy status and calculating the DNA index in neuroblastoma patients. 2, 3, 4 This method:
- Directly quantifies nuclear DNA content by measuring fluorescence intensity of DNA-binding dyes 3, 4
- Generates DNA histograms that display cell populations based on their DNA content 3
- Calculates the DNA index by comparing the DNA content of tumor cells to normal diploid cells (typically lymphocytes) 2, 5
- Can be performed on both fresh tumor samples and paraffin-embedded tissue 2, 3
Clinical Significance and Interpretation
The NCCN guidelines emphasize that ploidy status serves as a prognostic factor specifically for a small subset of patients, particularly infants. 1
Key prognostic distinctions:
- DNA index = 1 (diploid) is considered less favorable 1
- DNA index > 1 (aneuploid/hyperdiploid) is associated with better outcomes 1
- Near-triploid DNA content (DNA index 1.27-1.60) correlates with favorable prognosis in stage IVS neuroblastoma 5
- DNA aneuploidy is significantly more frequent in patients with lower clinical stage, younger age at diagnosis, and absence of MYCN amplification 2
Technical Considerations
Flow cytometry for DNA index determination:
- Requires adequate tumor cell numbers for accurate analysis 3
- Can distinguish tumor cells from normal lymphocytes through cell sorting based on DNA histogram peaks 3
- Provides stable tumor marker results regardless of tumor site (primary versus metastatic) or changes over time with therapy 4
- Successfully detects DNA aneuploidy in approximately 60% of neuroblastoma patients 4
Integration with Comprehensive Molecular Testing
While flow cytometry remains the method for DNA index assessment, the NCCN guidelines note that flow cytometry can also be used to assess other prognostic biomarkers (MYCN amplification status, segmental chromosomal aberrations) alongside ploidy, though it will not identify sequence variants in genes like ALK. 1
Important caveat: DNA ploidy has historically been used primarily in risk classification for infants, and its prognostic value is most relevant in this specific patient population rather than across all age groups. 1