Molecular Testing for Lipomatous Tumors: Critical Analysis and Test Recommendations Based on the Analysis of 405 Extremity-based Tumors

Abstract

Ancillary molecular testing has been advocated for diagnostic accuracy in the differentiation of lipomas from atypical lipomatous tumors/well-differentiated liposarcomas (ALT/WDL); however, the implications and specific indications for use are not well-established in the current literature. Herein, we extend previous findings by quantitatively evaluating the impact of molecular testing of lipomatous neoplasms in our routine clinical practice, how it modifies the historical perspective of their clinical course, and the effect of distinct surgical procedures in modulating the risk of local recurrence for these tumors after molecular classification. On the basis of these analyses, we suggest a specific set of basic recommendations for complementary molecular assessment in the diagnosis of lipomatous tumors. Four hundred and five lipomatous neoplasms located in the trunk and extremities were analyzed histologically and for the presence of 12q13-15 amplification on paraffin-embedded tissues by assessing MDM2/CPM amplification. Survival analyses were calculated with Kaplan-Meier and compared with the log-rank. Multivariate analysis was evaluated by the Cox regression method. The 405 tumors were histologically classified as ordinary lipoma (n=324), intramuscular lipoma (n=29), and ALT/WDL (n=52). The level of agreement between the histologic diagnosis and the molecular diagnosis was high (96%) but pathologists showed a tendency to overestimate cytologic atypia and the diagnosis of ALT/WDL (precision, 79%; accuracy, 88%). Molecular assessment led to a major diagnostic reclassification in 18 tumors (4%). Eleven of the tumors histologically classified as ALT/WDL were reclassified as ordinary lipoma (n=5) and intramuscular lipoma (n=6); none of which recurred. Seven ordinary lipomas were reclassified as ALT/WDL, 6 of which were larger than 15 cm and deeply located; 2 recurred locally. After molecular data, the 5-year local recurrence rates for ordinary lipoma, intramuscular lipoma, and ALT/WDL were 1%, 12%, and 44%, respectively. Multivariate analyses after molecular assessment showed tumor type and type of resection to be associated with the risk of local recurrence. Complementary molecular testing refines the histologic classification of lipomatous tumors and better estimates the impact of surgical procedures on the risk of local recurrence. Pathologists tend to overestimate the degree of cytologic atypia and the indiscriminate use of molecular testing should be avoided, especially for extremity-based tumors. Molecular testing should be considered for "relapsing lipomas," tumors with questionable cytologic atypia (even if widely excised), or for large lipomatous tumors (>15 cm) without diagnostic cytologic atypia.

Sensitivity of MDM2 amplification and unexpected multiple faint alphoid 12 (alpha 12 satellite sequences) signals in atypical lipomatous tumor

“…9 Our data support the findings of others and shows that there is a good correlation between microscopic diagnosis and MDM2 amplification status. [5][6][7][8][9][10] As in the study by Zhang et al 10 we found that we had a tendency to 'overcall' lipomas, whereas the risk of 'under-calling' an atypical lipomatous tumor (MDM2 amplification-positive) was much less. Specifically, we found that 2 of 86 (2%) tumors reported as lipomas exhibited MDM2 amplification, whereas 79 of 92 (87%) of the mature lipomatous tumors diagnosed as atypical lipomatous tumor harbored MDM2 amplification.…”

“…Our finding highlights the need for awareness of this chromosomal structural abnormality because it could be misinterpreted as gain of copy number of both centromere 12 and MDM2, which has occasionally been described in dedifferentiated liposarcoma, 29,30 but never in atypical lipomatous tumor. 5,[8][9][10] Our study shows that 4% (4/92) of atypical lipomatous tumors and 10% of the dedifferentiated liposarcomas (2/20) as well as one low-grade myxofibrosarcoma revealed multiple faint alphoid 12 signals. All seven tumors with these signals also harbored CDK4 amplification regardless of the MDM2 amplification status.…”

“…[5][6][7][8][9][10]20 As a consequence, the identification of this molecular abnormality is advocated as a useful ancillary diagnostic marker, and can be considered 100% specific in the appropriate clinical and histological context. 9 Our data support the findings of others and shows that there is a good correlation between microscopic diagnosis and MDM2 amplification status.…”

“…2 A number of studies have shown that there is a strong correlation between the presence of supernumerary ring or giant marker chromosomes, derived from chromosome 12q13-15 where MDM2, CDK4, SAS, HMGIC and other genes are located, and the morphological features of atypical lipomatous tumors and dedifferentiated liposarcomas. These genetic abnormalities, originally reported using cytogenetics, 3,4 and subsequently by reverse transcription polymerase chain reaction, [5][6][7] fluorescence in situ hybridization (FISH), [8][9][10] and later with antibodies to MDM2 and CDK4, 5,8 demonstrated that MDM2 amplification occurs consistently in atypical lipomatous tumor in which CDK4 is also frequently amplified. In contrast, other genes in the chromosomal region 12q13-15 are less commonly associated with copy number gain 11,12 and in a small number of cases CDK4 amplification has been reported in the absence of MDM2 copy number gain.…”

Magnetic Resonance Imaging Assessment of Lipomatous Soft-tissue Tumors

“…In particular, MDM2 has been identified as the gene most frequently amplified in ALT/WDLS. Others, however, have found a trend for overdiagnosis as a result of excessive use of immunohistochemistry, which should be reserved for doubtful forms, such as tumors >15 cm without cytologically demonstrated atypia or cancer with questionable cytologic atypia (8). Therefore, a multidisciplinary approach (clinical-radiological -pathological) is essential for the best diagnostic classification of these tumors.…”