Analysis And Interpretation Of Results

The methods to analyze chromosomes are numerous, sophisticated, and vary among laboratories. Today, the cytogenetic laboratory must be proficient with many forms of culture techniques, more than 20 different chromosome staining methods, and have expertise with fluorescence-labeled DNA probes and in situ hybridization (FISH) (18,21-24). Typical examples are shown in Fig. 10-1. Metaphases are usually stained with G-banding, but other staining methods are frequently employed as needed. Twenty metaphases are typically examined for structure and number of chromosomes, but structural chromosome abnormalities are subtle and can be missed. In cases where mosaicism is suspected, 30 or more metaphases are often analyzed but true mosaicism still is sometimes missed because of metaphase sampling error. Representative metaphases are photographed and karyotypes are prepared from at least two cells.

In the case of malignant neoplasms, two or more metaphases with the same structural abnormality or extra chromosome, or three or more metaphases lacking the same chromosome, are regarded as minimal evidence for the presence of an abnormal clone (25). In some neoplastic disorders, abnormal clones may be missed when the malignant cells are not dividing (9). In solid tumors, numerous complex chromosome anomalies sometimes make it difficult to identify specific chromosome abnormalities associated with certain neoplasms, but it is usually possible to identify the presence of an abnormal clone (26).

The results of chromosome studies are usually provided according to a complicated but well-defined nomenclature (25). In addition, cytogeneticists usually provide a narrative report that can be readily appreciated by a physician who is not expert in genetics. A cytogenetic report is usually issued after about 5-7 d for peripheral blood and bone marrow, 2-4 wk for fibroblast cultures, and about 10 d for solid tumors.

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