Non-mesenchymal Mimics of Sarcoma

Primary Soft-Tissue Lymphomas: MRI Features Help Discriminate From Other Soft-Tissue Tumors

OBJECTIVES

MRI presentation of extra-nodal soft-tissue lymphomas (STLs) is scarcely reported and lacks of comparison with other soft-tissue tumors (STTs) including sarcomas (STS). Yet, suggesting this diagnosis on MRI would considerably reduce diagnostic intervals. Our aim was to investigate if conventional MRI could discriminate STLs from other STTs.

METHODS

MRIs of STL patients were compared with those of patients addressed to a sarcoma reference center for the diagnosis of a STT. MRI characteristics depicting the tumor (size, signal, habitats, shape, surrounding tissues) were reported. Uni- and multivariate associations with STL diagnosis were evaluated in the entire cohort, and in the subgroups of benign and malignant STTs patients. Diagnostic performances of MRI features combinations were tested.

RESULTS

We included 39 patients with STLs (median age: 69 years) and 368 patients with other STTs (122 benign STTs and 246 STS; median age: 58 years). Six MRI features were independent predictors of STL compared to all other STTs: intermediate SI on T1-WI, homogeneous enhancement (without necrotic areas), no blood signal, no fibrotic signal, no peritumoral enhancement and lack of abnormal intra- and peritumoral vasculature (p-value range: <0.0001-0.0163). Their simultaneous presence had a sensitivity of 0.88 (0.71-0.96) and a specificity of 0.88 (0.84-0.91). Other relevant MRI features were: no fat signal to discriminate against STS (p = 0.0409), the infiltrative growth pattern and the vessel and nerve encasement to discriminate against benign STTs (p = 0.0016 and 0.0011, respectively).

CONCLUSION

Our research demonstrates that conventional MRI can help discriminating STLs from other STTs. Indeed, radiologists can help suggesting the possible diagnosis of STL, which could speed-up the subsequent proper histopathological analysis in light of MRI findings.

Practical Application of Cytology and Core Biopsy in the Diagnosis of Mesenchymal Tumors

Soft tissue neoplasms are increasingly being sampled by core needle biopsy and fine-needle aspiration (FNA), and these small biopsy specimens pose unique diagnostic challenges. Many advances in ancillary testing enable detection of characteristic immunophenotypes and molecular alterations, allowing accurate classification of soft tissue tumors in these small biopsy samples. This review outlines pattern-based diagnostic approaches to core biopsies and FNAs of soft tissue neoplasms, including formulation of practical differential diagnoses and relevant application of ancillary tests.

NKX2.2 immunohistochemistry in the distinction of Ewing sarcoma from cytomorphologic mimics: Diagnostic utility and pitfalls

BACKGROUND

Ewing sarcoma (ES) is a round cell sarcoma that can be challenging to diagnose on cytologic material given its significant overlap with numerous mesenchymal, epithelial, and lymphoid cytomorphologic mimics. The objective of this study was to assess the utility of a novel marker, NKX2.2, in the diagnosis of ES in cytologic material and its ability to distinguish ES from its mimics.

METHODS

NKX2.2 immunohistochemistry was performed on cell blocks from 107 fine-needle aspirations, and nuclear expression was scored semiquantitatively for extent and intensity. The study cohort included ES (n = 10), well differentiated neuroendocrine tumor (n = 20), melanoma (n = 11), Merkel cell carcinoma (n = 10), small cell carcinoma (n = 10), alveolar rhabdomyosarcoma (n = 2), spindle cell/sclerosing rhabdomyosarcoma (n = 2), synovial sarcoma (n = 12), solitary fibrous tumor (n = 2), chronic lymphocytic leukemia (n = 10), lymphoblastic lymphoma (n = 11), adenoid cystic carcinoma (n = 6), and CIC-rearranged sarcoma (n = 1).

RESULTS

NKX2.2 had high sensitivity (100%) and moderate specificity (85%) for the diagnosis of ES in cytologic material. NKX2.2 expression also was present in a subset of mesenchymal and epithelial mimics, and staining was most commonly observed in small cell carcinoma (80%) and well differentiated neuroendocrine tumor (45%). Among mesenchymal mimics, 42% exhibited NKX2.2 expression. NKX2.2 staining was absent in melanoma, adenoid cystic carcinoma, and lymphoproliferative neoplasms.

CONCLUSIONS

NKX2.2 is a highly sensitive but only moderately specific marker for ES. Neuroendocrine neoplasms exhibit variable NKX2.2 expression and remain a significant potential diagnostic pitfall. Thus, NKX2.2 expression should be interpreted in the context of an appropriate immunohistochemical panel (and often with confirmatory molecular testing) for the accurate diagnosis of ES.