Although soft tissue masses (STMs) account for approximately 1% of malignant lesions, small lesions are often assumed to be benign. Current guidelines include resection biopsy for lesions with a diameter of less than 3 cm., which creates the risk of failing to achieve tumor-free margins.
"Not only do we need to know the percentage of malignancies in small soft tissue masses, we also need to be able to estimate the distribution of expected entities," said researcher Felix Gassert, MD, a radiologist at the Technical University of Munich, Germany.
In his RSNA 2020 session, Dr. Gassert discussed the findings of recent research on the correlation of malignancy rate and tumor size and location. "What we found is that the rate of malignancy decreased significantly with tumor size in both superficial and deep STMs," he said.
Malignancy Rates and Diameter, Entity and Location
The study comprised 1,753 patients presenting with a STM over a 10-year period at Klinikum rechts der Isar, a large tertiary referral center at the Technical University of Munich.
After a final histopathological diagnosis, all lesions were categorized as benign, malignant or non-neoplastic, with the maximum diameter determined on MRI.
The study also assessed tumor localization (head/neck, trunk, upper extremity, lower extremity, hand, foot) and depth (superficial, deep).
Out of the 1,753 patients reviewed, 870 showed an STM with a diameter of less than 5 cm. and were therefore included in the study.
"We found that the rate of malignancy decreased significantly with tumor size in both superficial and deep soft tissue masses," Dr. Gassert said.
Results showed that the most common benign entities were tenosynovial giant cell tumor, lipoma and schwannoma. On the malignant side, the most common entities were undifferentiated pleomorphic sarcoma, liposarcoma and myxofibrosarcoma. The most common non-neoplastic entities were ganglion, pseudotumor and bursitis.
"One of the key findings is that the malignancy rate for all lesions smaller than 5 cm. was approximately 22%, with the malignancy rate significantly decreasing with lesion diameter," Dr. Gassert said. "That said, the malignancy rate was still over 15% for lesions less than 2 cm."
Approximately 20% of lesions were superficial while the remaining 80% were classified as being deep in relation to the fascia.
"Despite the different distribution of entities in superficial and deep lesions, no significant difference in malignancy rate was observed," Dr. Gassert added.
The study also determined that malignancy rates change with lesion location, although no location was without malignant lesions.
"The lowest malignancy rate was observed in the foot region and the highest in the head and neck region," Dr. Gassert said.
Achieving Tumor-Free Margins
Ultimately, the study demonstrates the need to consider even the smallest lesions as potentially malignant and to develop a treatment plan accordingly.
"Our study helps us better estimate the entity and probability of malignancy of small, superficial and deep soft tissue masses," Dr. Gassert concluded. "In doing so, we will be better positioned to choose between biopsy and primary resection and, thus, achieve tumor-free margins."
For More Information:
View the RSNA 2020 session Imaging of Soft Tissue Masses: Distribution of Entities and Rate of Malignancy in Small Lesions — SSMK10 at RSNA2020.RSNA.org.
