Interpretive Handbook

Test 89366 :
CPM, 12q15, for Well-Differentiated Liposarcoma/Atypical Lipomatous Tumor, FISH

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

The histological discrimination of well-differentiated liposarcoma/atypical lipomatous tumor (WDL/ALT) from lipoma can be diagnostically challenging. However, standard cytogenetic identification of ring and giant rod chromosomes strongly support the diagnosis of WDL/ALT. These abnormal chromosomes are mainly composed of amplified sequences derived from chromosome bands 12q13-15, and contain several amplified genes including MDM2, CPM, CDK4, and TSPAN31. MDM2 is amplified in >99% of WDL, and up to 30% of other types of sarcomas. The CPM gene encodes carboxypeptidase M, a membrane-bound arginine/lysine carboxypeptidase. CPM is located only 11 kb upstream from MDM2, and is consistently coamplified with MDM2 in WDL/ALT.(1) Similar to MDM2, this gene has been observed to be amplified in virtually all cases of WDL/ALT, but not in lipomas.

Useful For Suggests clinical disorders or settings where the test may be helpful

Supporting a diagnosis of well-differentiated liposarcoma/atypical lipomatous tumor

Interpretation Provides information to assist in interpretation of the test results

An interpretive report will be provided.


A neoplastic clone is detected when the percent of cells with an abnormality exceeds the normal reference range for the CPM FISH probe (positive result).


A positive result is consistent with amplification of the CPM gene locus on 12q13-15 and supports the diagnosis of well-differentiated liposarcoma/atypical lipomatous tumor (WDL/ALT).


A negative result is consistent with absence of amplification of the CPM gene locus on 12q13-15. However, negative results do not exclude the diagnosis of WDL/ALT. Amplification varies in individual tumors and among different cells in the same tumor.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Reliable results are dependent on adequate specimen collection and processing. This test has been validated on formalin-fixed, paraffin-embedded tissue; other types of fixatives are discouraged. Improper treatment of tissues, such as decalcification, may cause FISH failure.  

Clinical diagnosis and/or therapy should not be based solely on this assay. The results should be considered in conjunction with clinical information and/or additional diagnostic tests.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

0-9% amplified cells

Clinical References Provides recommendations for further in-depth reading of a clinical nature

1. Erickson-Johnson MR, Seys AR, Roth CW, et al: Carboxypeptidase M: a biomarker for the discrimination of lipoma from liposarcoma. Mod Pathol 2009 Dec;22(12):1541-1547

2. Jacob E, Erickson-Johnson MR, Wang X, et al: Assessment of MDM2 amplification using fluorescence in situ hybridization on paraffin-embedded tissue discriminates atypical lipomatous tumors from lipomas. Mod Pathol 2006;19:13A