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"&amp;lt;p&amp;gt;The Philadelphia chromosome is &amp;lt;a href=&amp;quot;https://www.verywell.com/chromosome-translocation-2252083&amp;quot; data-component=&amp;quot;link&amp;quot; data-source=&amp;quot;inlineLink&amp;quot; data-type=&amp;quot;internalLink&amp;quot; data-ordinal=&amp;quot;1&amp;quot;&amp;gt;a specific finding in the genes&amp;lt;/a&amp;gt; of a person\u2019s white blood cells \u2013 a finding that has implications for leukemia. It most commonly comes up in reference to \u201CPhiladelphia chromosome-positive leukemia,\u201D or it might be \u201CPhiladelphia-chromosome-positive &amp;lt;a href=&amp;quot;https://www.verywell.com/what-is-chronic-myelogenous-leukemia-cml-2252069&amp;quot; data-component=&amp;quot;link&amp;quot; data-source=&amp;quot;inlineLink&amp;quot; data-type=&amp;quot;internalLink&amp;quot; data-ordinal=&amp;quot;2&amp;quot;&amp;gt;chronic myeloid leukemia&amp;lt;/a&amp;gt;\u201D or \u201CPhiladelphia chromosome-positive acute lymphoblastic leukemia.\u201D&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Or, there might even be references to \u201Cvariant Philadelphia translocations,\u201D and \u201CPhiladelphia chromosome-negative chronic myeloproliferative disease.\u201D &amp;lt;em&amp;gt;So you see, the Philadelphia chromosome is a specific genetic change that has become a sort of landmark \u2013 useful for identifying certain cancers for its presence, and other cancers for its absence.&amp;lt;/em&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;h3&amp;gt;&amp;lt;strong&amp;gt;Chromosome Refresher&amp;lt;/strong&amp;gt;&amp;lt;/h3&amp;gt;&amp;lt;p&amp;gt;We all kind of know what chromosomes are from high school science, even if we became poets or politicians in real life. However, as the years march on, a refresher seems in order.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled -- many times -- around proteins called histones. Unless a cell is dividing in two, chromosomes are not visible within the nucleus\u2014not even under a microscope\u2014that\u2019s because in a normal cell the DNA is not packed up and away so neatly, since it is being used by the cell at many different locations. However, the DNA that makes up chromosomes becomes very tightly packed during cell division and is then visible under a microscope as a chromosome.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Each chromosome has its own characteristic shape, and the location of specific genes can be found in relation to the shape of a chromosome. When all the genetic material in the cell of a human being gets packaged up into suitcase-chromosomes, there are 23 pairs of chromosomes, for a total of 46 chromosomes in each cell. In fact, different species of plants and animals have differing set numbers of chromosomes. A fruit fly, for example, has four pairs of chromosomes, while a rice plant has 12 and a dog, 39.&amp;lt;/p&amp;gt;&amp;lt;h3&amp;gt;&amp;lt;strong&amp;gt;The Philadelphia Chromosome&amp;lt;/strong&amp;gt;&amp;lt;/h3&amp;gt;&amp;lt;p&amp;gt;The Philadelphia chromosome has a story and a setting, but for practical purposes, it can be defined as an abnormality of chromosome 22 in which part of chromosome 9 is transferred to it. In other words, a piece of chromosome 9 and a piece of chromosome 22 break off and trade places. When this trade takes place, it causes trouble in the genes \u2013 a gene called \u201Cbcr-abl\u201D is formed on chromosome 22 where the piece of chromosome 9 attaches. The changed chromosome 22 is called the Philadelphia chromosome.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Bone marrow cells that contain the Philadelphia chromosome are often found in chronic myelogenous &amp;lt;a href=&amp;quot;https://www.verywell.com/major-differences-between-leukemia-and-lymphoma-2252555&amp;quot; data-component=&amp;quot;link&amp;quot; data-source=&amp;quot;inlineLink&amp;quot; data-type=&amp;quot;internalLink&amp;quot; data-ordinal=&amp;quot;3&amp;quot;&amp;gt;leukemia&amp;lt;/a&amp;gt; and sometimes found in &amp;lt;a href=&amp;quot;https://www.verywell.com/what-is-the-most-common-childhood-leukemia-2252286&amp;quot; data-component=&amp;quot;link&amp;quot; data-source=&amp;quot;inlineLink&amp;quot; data-type=&amp;quot;internalLink&amp;quot; data-ordinal=&amp;quot;4&amp;quot;&amp;gt;acute lymphocytic leukemia&amp;lt;/a&amp;gt;.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;As part of their assessment, doctors will look for the presence of the Philadelphia chromosome to help determine if a patient is affected by particular types of leukemia.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The Philadelphia chromosome is only found in the affected blood cells. Because of the damage to the DNA, the Philadelphia chromosome results in the production of an abnormal enzyme called a tyrosine kinase. Along with other abnormalities, this enzyme causes the cancer cell to grow uncontrollably.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Doctors will look for the presence of this abnormality when they are examining samples from your &amp;lt;a href=&amp;quot;https://www.verywell.com/how-is-a-bone-marrow-test-done-2252452&amp;quot; data-component=&amp;quot;link&amp;quot; data-source=&amp;quot;inlineLink&amp;quot; data-type=&amp;quot;internalLink&amp;quot; data-ordinal=&amp;quot;5&amp;quot;&amp;gt;bone marrow aspiration and biopsy&amp;lt;/a&amp;gt; to help make a proper diagnosis.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The identification of the Philadelphia chromosome in the 1960s led to major advancements in the treatment of CML. This laid the foundation for a new era of CML therapy called &amp;amp;#34;tyrosine kinase inhibitors,&amp;amp;#34; such as Gleevac (imatinib mesylate) and Sprycel (dasatinib)&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;strong&amp;gt;&amp;lt;sub&amp;gt;Sources&amp;lt;/sub&amp;gt;&amp;lt;/strong&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;sub&amp;gt;Goldman, J. and Daley, G. (2007). Chronic Myeloid Leukemia. In Melo, J., and Goldman, J. (Eds.) &amp;lt;em&amp;gt;Myeloproliferative Disorders&amp;lt;/em&amp;gt; (pp.1-13). New York. Springer.&amp;lt;/sub&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;sub&amp;gt;Sherbenou, D. and Druker, B. &amp;amp;#34;Applying the discovery of the Philadelphia chromosome&amp;amp;#34; &amp;lt;em&amp;gt;The Journal of Clinical Investigation&amp;lt;/em&amp;gt; August 2007 117:2067-74.&amp;lt;/sub&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;sub&amp;gt;Adamson PC. Improving the Outcome for Children With Cancer: Development of Targeted New Agents. CA Cancer J Clin. 2015;65(3):212-220.&amp;lt;/sub&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;sub&amp;gt;Nowell PC. Discovery of the Philadelphia chromosome: a personal perspective. Journal of Clinical Investigation. 2007;117(8):2033-2035.&amp;lt;/sub&amp;gt;&amp;lt;/p&amp;gt;"^^<http://www.w3.org/2001/XMLSchema#string>
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