Objective Whether H3.3 K36M mutation (H3K36M) could be an approach if the diagnosis of chondroblastoma (CB) patients was indistinct and it was suspected to be unclear clinically. Methods We reviewed and compared our clinical experiences of CB cases and some suspected cases, which were not diagnosed distinctly, between 2013 to 2019. A total of 15 male and four female cases included in this study were seperated into two groups, CB group and suspected case (SC) group. The CB group included 13 men and 3 women, with an age range from 9 to 54 (mean age, 22 years old). The SC group included two men and one woman, with the age range from 13 to 25 (mean age, 19 years old). In both groups the patients had been followed-up until December 2019 and none of the patients had prior treatment history. We evaluated the clinical complaints, radiological features, and clinical-histological features of the cases and performed an immunohistochemical (IHC) study to detect whether the H3K36M expression of cases was different, consistent with a gene-mutation analysis. Results In both groups, the radiologic features of both groups appeared as round low-density shadow with a clear edge, pathologic features showed diffuse proliferation of neoplastic cells with multinuclear giant cells. The radiological tumor size of CB group and SC group showed little difference, which was about 29.0*21.6 mm. Clinical-immunohistochemical features of both groups showed chondroid matrix inside with naive tumor cells, multinucleated giant cells, and ground substance cells. Most of them showed chondro-related antibody positive (12 cases) but some of them showed S-100 negative (four cases). The clear difference of both groups was the result of H3K36M IHC study and gene analysis. In our cases, the CB group showed diffuse H3K36M positive and the SC group showed negative. The gene mutation analysis revealed that H3K36M-positive CB patients had K36M mutation, which were not found in the SC group. Sanger sequencing showed an A > T substitution at codon 36 of histone H3F3B. No other types of histone H3 mutation was detected in the CB group. Particularly, one of the suspected cases showed a G34W mutation was confirmed to be a giant cell tumor of bone (GCTB). Conclusions Our study showed H3K36M immunohistochemistry and gene mutation analysis were specific clinical diagnostic tools to distinguish suspected CB from other giant cell-rich or cartilage matrix-diffuse bone tumors. The clinical-radiological and histomorphological features of patients gave suggestions on whether the H3K36M IHC and gene analysis should be required.

H3.3 K36M Mutation as a Clinical Diagnosis Method of Suspected Chondroblastoma Cases.

35-year-old woman suffered prolonged pain in the left shoulder, where an aggressively growing tumor of the proximal humerus was revealed thereafter. The lesion caused massive osteolysis of the metaepiphysis with cortical disruption, but no soft tissue extension was evident. Given the unsatisfactory effect, the ongoing neoadjuvant chemotherapy was prematurely ceased and the resection 13 cm long segment of bone with modular prosthesis replacement followed. Histologically, clear-cut malignant tumor with both the presence of numerous reactive osteoclast-like giant cells and geographic structural deposition of chondroid matrix bore a close resemblance to chondroblastoma. Dominant cellular composition formed solid mosaic clusters of large, atypical, frequently binucleated cells with voluminous eosinophilic cytoplasm. Impressive nuclear pleomorphism was accentuated by both the grooving and atypical mitotic figures. Thorough sampling disclosed limited, but sharply contrasting parts, where biphasic arrangement of small uniform stromal elements together with regularly distributed, reactive osteoclasts suggested putative precursor giant cell lesion. Except the osteoclasts, all matrical and stromal cells were strongly SOX9 and D2-40 positive; in contrary desmin, SATB2, S100 and p63 yielded completely negative results. Detected H3F3A c.103GgT mutation in exon 2 finally established true nature of that peculiar neoplastic proliferation and lead to descriptive term of primary chondroblastoma-like malignant giant cell tumor. In the setting of all the microscopic variability, histogenesis and complex differential diagnosis of skeletal (malignant) giant cell lesions, there are discussed e.g. aggressive/malignant chondroblastoma, chondroblastoma-like osteosarcoma or giant cell-rich osteosarcoma and practical impact of specific mutational analysis results as well.

Zuzana Věcková

Papers

Chondroblastoma-like primary malignant giant cell tumor of the humerus - a case report.