Deletions of the long arm of 5q are the most common rearrangements in AML and MDS; chromosome 5 abnormalities account for approximately 40% or more of treatment-related MDS;

Deletions occurring within 5q (5q31-q33) occur in 10-15% of MDS patients and have a favorable prognosis;

5q deletion syndrome, a separate molecular type added by WHO in 2000, has a predominance of female patients and a better prognosis;

Thalidomide works well in those with 5q deletion abnormalities. Testing for 5q deletion and mutations in the p53 gene is required before and during use.