This type of aberration is also known as Copy Number Gains or Amplification.
An HSR is one type of change in a chromosome's structure which is frequently observed in the nucleus of human cancer cells.
In the region of a chromosome where an HSR occurs, a segment of the chromosome, which presumably contains a gene or genes that give selective advantage to the progression of the cancer, is amplified or duplicated many times.
The homogenously staining region was first observed in chromosome 2 by June Biedler and Barbara Spengler in cells that had been made resistant to methotrexate.
The HSR was found to due to the amplification of the DHFR gene.