Counting the nucleolar organizer region-associated proteins is a prognostic clue of malignant melanoma

The nucleolar organizer regions (NORs) are chromosomal loops of DNA to which acidic proteins are associated that are seen by silver staining as black dots within the nucleoli (hereafter, these silver-staining NORs will be referred to as AgNORs). As their size and number reflect cell and nuclear activity, their counting in paraffin sections is regarded as a useful tool for diagnosing and prognosing malignant tumors. We counted AgNORs in 98 patients with stage I melanoma, followed up to an average of 73 months, to verify whether the number of AgNORs is of prognostic value.

The number of AgNORs averaged 2.792 +/- 0.901 in the 64 patients without metastases and 4.889 +/- 1.403 in the 34 with metastases. In patients with counts higher than 3.62, there was an 82% probability of metastases developing.

The technique is fast, simple, and reproducible with easily available reagents and standard light microscopy. In our population, AgNOR counts constituted a more accurate prognostic indicator than Clark's level and Breslow's thickness. Confirmation in a new population is needed.