Tissue Profiling by MALDI Mass Spectrometry Distinguishes Clinical Grades of Soft Tissue Sarcomas

Soft tissue sarcomas are rare, heterogeneous, mesenchymal tumors that have been poorly classified. The heterogeneity of these aggressive tumors has made consistent tumor grading difficult and accurately predicting the behavior of the tumor based on the histological subtype and grade has been challenging. Molecular profiling of proteins in tissues may present a new avenue for distinguishing clinical grades and overall tumor aggressiveness. Direct tissue analysis using matrix-assisted laser desorption ionization mass spectrometry is a new technology that permits rapid detection of hundreds of proteins from intact tissues. We have employed this technology to profile human soft tissue sarcomas to discover protein biomarkers that distinguish tumor grade. Profiling was accomplished on histologically-stained tissue sections, allowing highly reproducible spectra for each sarcoma grade to be obtained. Forty-two tissue specimens were analyzed in this manner. Several proteins specific for high-grade sarcomas were identified and confirmed with immunohistochemistry. Proteins present in control tissue, that are suppressed by soft tissue sarcomas, were also identified. Soft tissue sarcomas (STS) are devastating cancers that account for 0.63% of total cancer cases and 1.15% of cancer deaths in the United States, with a five-year survival rate of approximately 60% after diagnosis (1, 2) In 2004, approximately 8,680 new cases were diagnosed in the United States, and 3,660 deaths are predicted from STS. STS are heterogeneous, mesenchymal tumors that arise from various origins, many of which are idiopathic (3). The tumors develop mostly as asymptomatic masses originating in an extremity, but can occur anywhere in the body, such as the trunk, retroperitoneum, or the head and neck (4). The current criteria set by The American Joint Committee on Cancer stages STS on histological grade, tumor size and depth, and presence of distant metastases. The most common site of metastasis is the lung parenchyma, and survival after pulmonary metastasis is <10% at two years post diagnosis (2). Pulmonary metastasis generally occurs within two to three years after diagnosis of the primary tumor (3). Despite improvements in control of local disease, mortality remains significant for more than 50% of the patients diagnosed with high-grade STS. Currently, over fifty histological subtypes of STS exist, the most common being malignant fibrous histiocytoma (28%), leiomyosarcoma (12%), liposarcoma (15%), synovial sarcoma (10%) and malignant peripheral nerve sheath tumors (6%) (5). The heterogeneity, both intratumoral and extratumoral, of these aggressive tumors has made diagnosis, staging and treatment difficult. Anatomic pathology has been used since 1977 to categorize STS, regardless of whether or not the morphological differences indicate a certain level of tumor invasiveness or metastatic potential (6). Indeed, these unique clinical features, associated with the large variety of STS, have given rise to many histological subtypes, making the staging and grading criteria used to predict patient outcome controversial. It has been established that STS is misclassified in up to 25% to 40% of cases (7-10). Moreover, the current staging and grading criteria are not applicable to all types of STS and have no prognostic value for several histological subtypes (11). Therefore, treatment regimens remain extremely controversial due to this overwhelming, and often inaccurate, classification scheme. For this reason, the need for more objective molecular and biochemical protein biomarkers is required to improve the accuracy of conventional anatomic and histological assessments. In this respect, it is also reasonable to presume that more generalized grades exist that are based on specific protein expression profiles. These profiles may translate into disease