Federation Nationale des Centers de Lutte Contre le Cancer grading of soft tissue sarcomas on needle core biopsies using surrogate markers

Needle core biopsy (NCB) of soft tissue sarcomas (STSs) presents problems for French Federation Nationale des Centers de Lutte Contre le Cancer (FNCLCC) histological grading because small sample size hinders determination of necrosis and mitotic activity. We graded 53 STSs on NCB using a modified FNCLCC grading system that substitutes Ki-67 immunoexpression for mitotic count and uses a radiological assessment of necrosis, and compared the results with those obtained by conventional FNCLCC grading of the corresponding untreated, surgically resected specimen. Forty-eight of the 53 tumors were classified as malignant on NCB (concordance = 91%). The modified FNCLCC grade correctly separated high-grade (grades II and III) from low-grade sarcomas in 70% of cases and predicted the traditional FNCLCC grade given to the resected specimen in 49% of cases. Ki-67 scores of 2 or 3 were observed in 5 tumors classified as low-grade neoplasms on NCB but upgraded to a high-grade dedifferentiated liposarcoma on resection. Underestimated NCB grades were commonly encountered with lipomatous tumors due to sampling error, whereas Ki-67 or radiologic necrosis scores higher than the corresponding histological scores were responsible for the vast majority of overestimated NCB grades. Our FNCLCC grading scheme replacing conventional mitosis counting and histologic assessment of necrosis with surrogate markers is useful in separating high- and low-grade STSs on NCB for STS treatment planning. High Ki-67 rate should raise suspicion of a higher-grade component, particularly with fatty tumors.