Histone H3K36M mutation and trimethylation patterns in chondroblastoma

Abstract

Aims: Histones are essential components of chromatin, and mutations in histones lead to alterations in methylation and acetylation, which play an important role in tumorigenesis. Most of the chondroblastomas harbour the H3K36M mutation. With the availability of a mutation-specific antibody, we sought to assess the sensitivity of this antibody and the alterations of histone methylation in a series of chondroblastoma cases.

Methods and results: Immunohistochemical staining with antibodies against H3K36M, trimethylated histones (H3K27me3 and H3K36me3) and an osteoblastic marker (SATB2) was performed on 27 chondroblastomas from 27 patients. The clinical and radiological characteristics of each patient were reviewed. All 27 tumours showed typical radiological and histological features of chondroblastoma, with a subset of cases showing secondary aneurysmal bone cyst changes (11/27), giant-cell-rich foci (4/27), and matrix-rich areas mimicking chondromyxoid fibroma (1/27). All except one case (26/27, 96%) showed positive H3K36M immunostaining (nuclear). In the majority of cases, there was a diffuse staining pattern. Immunohistochemical staining for H3K27me3 and H3K36me3 showed a heterogeneous staining pattern in all cases, regardless of mutation status. None of the cases showed loss of positivity or diffuse positivity. Focal or diffuse SATB2 expression was seen in 21 of 26 tumours (81%).

Conclusion: Our results demonstrate that the vast majority of chondroblastomas are positive for H3K36M by immunohistochemical analysis, confirming its diagnostic value. H3K27me3 expression and H3K36me3 expression are heterogeneous in these tumours.

Keywords: H3K27me3; H3K36M; H3K36me3; SATB2; chondroblastoma; histone; methylation; mutation.

Fig. 1

A representative case of chondroblastoma with positive H3K36M immunostaining. The patient was a 11-year-old male. (A) Radiograph showed an epiphyseal lytic tumor(arrow). (B) MRI T1- and (C) T2-weighted fat-suppressed images showed the tumor surrounded by edema (*). The tumor was curetted and cemented. The patient was followed for 58 months and (D) radiograph showed no recurrence. (E) Histologically, the tumor was composed of sheets of uniform cells with focal chondroid differentiation and scattered multi-nucleated giant cells (200x). (F) The tumor cells were oval to polygonal with well-defined pink cytoplasm and cleaved nuclei (400x). (G) The tumor cells showed strong nuclear staining of H3K36M (200x). Immunostaining for methylated histones, (H) H3K27me3 and (I) H3K36me3, showed heterogeneous staining in both the mononuclear tumor cells and the multi-nucleated giant cells (200x). (J) SATB2 was positive in a subset of the tumor cells (200x).

Fig. 2

Chondroblastomas with focal aneurysmal bone cyst-like changes (A-C), giant cell rich area (D-F), and matrix rich area (G-I). All tumors were positive for H3K36M immunostaining. H3K36M positive cells are seen in ABC-like areas (arrow) (C).

Fig. 3

A case of chondroblastoma with lung metastasis. The patient was a 13-year-old male. (A) Pre-op radiograph showed a lytic ischial lesion(arrow). (B, C) Serial CT exams in 2 months showed increased size and cortical destruction of the tumor(arrows). The tumor was treated by embolization, curettage and bone grafting. (D) Histologically, the tumor was composed of sheets of uniform cells with chondroid differentiation, aneurysmal bone cyst-like change, and frequent multi-nucleated giant cells (100x). (E) The tumor cells showed typical morphology of chondroblasts (400x) and (F) were strongly positive for H3K36M (200x). Three months after curettage, (G) radiograph showed recurrent tumor (arrows). (H) MRI T2-weighted, and (I) T1-weighted FS post-contrast images showed fluid levels (arrowheads) and enhancing components(arrow) in the tumor. (J) The recurrence was biopsied and tumor was again positive for H3K36M immunostaining. At 11 months after the surgery, (K) CT showed pulmonary nodules(arrows). (L) Needle core biopsy of a lung nodule confirmed metastatic chondroblastoma, which showed similar morphology as that seen in the primary tumor (400x) and (M) tumor cells were positive for H3K36M immunostaining (400x).