Immunohistochemical expression of H3.3 G34W in 100 giant cell tumors of bone and its diagnostic mimics, including its value in resolving uncommon diagnostic scenarios: A single institutional study at a tertiary cancer referral center, India.

BACKGROUND: There can be a diagnostic challenge in differentiating giant cell tumor of bone (GCTB) from its mimics. Lately, histone H3F3A (Histone 3.3) G34W has been identified as a promising immunohistochemical marker. AIMS: This study was aimed at evaluating H3.3 G34W immunostaining in 100 GCTBs, including its value in resolving diagnostic dilemmas. MATERIALS AND METHODS: Immunohistochemical staining for H3.3 G34W was graded in terms of staining intensity (1+ to 3+) and the percentage of tumor cells showing crisp nuclear staining. RESULTS: One hundred GCTBs occurred in 58 males and 42 females (M: F ratio = 1.3), of 7-66 years age (average = 31.3, median = 28), commonly in distal femur (26), followed by proximal tibia (17), distal radius (12), proximal humerus (7), metacarpals (7), sacrum (6), proximal fibula (6), and relatively unusual sites (19), including a single multicentric case. Out of 92 GCTBs, wherein H3.3 G34W immunostaining worked, 81 (88.1%) showed positive staining in the mononuclear cells, including tumors with fibrous histiocytoma-like areas, sparing osteoclast-like giant cells, with 3+ staining intensity in 65/81 (80%) tumors. All 7/7 (100%) malignant GCTBs showed positive staining, including the pleomorphic/sarcomatous cells. All 7/7 (100%) metastatic GCTBs showed positive immunostaining. Seven out of 10 post-denosumab treated GCTBs showed positive H3.3 G34W immunostaining in the residual mononuclear cells. None of the other 37 "giant cell-rich" lesions displayed H3.3 G34W immunostaining. Four of 9 GCTBs tested for H3.3 G34W mutation showed positive results. CONCLUSIONS: The diagnostic sensitivity and specificity of H3.3 G34W for GCTB were 88.1% and 100%, respectively. This constitutes one of the first reports from our country, further validating the diagnostic value of H3.3 G34W in differentiating GCTB, including metastatic and malignant forms from its mimics, including small biopsy samples. Its value in various diagnostic dilemmas is presented and utility in identifying residual tumor cells in post-denosumab treated GCTBs is worth exploring.

Identification of genome-wide binding sites of heat shock factor 1, Hsf1, under basal conditions in the human pathogenic yeast, Candida albicans.

The master regulator of thermal stress response, Hsf1, is also an essential determinant for viability and virulence in Candida albicans. Our recent studies highlighted that apart from ubiquitous roles of Hsf1 at higher temperatures, it also has myriad non-heat shock responsive roles essential under iron deprivation and drug defense. Here, we further explored its implications in the normal cellular functioning, by profiling its genome-wide occupancy using chromatin immuno-precipitation coupled to high-density tiling arrays under basal and iron deprived conditions. Hsf1 recruitment profiles revealed that it binds to promoters of 660 genes of varied functions, under both the conditions, however, elicited variability in intensity of binding. For instance, Hsf1 binding was observed on several genes of oxidative and osmotic stress response, cell wall integrity, iron homeostasis, mitochondrial, hyphal and multidrug transporters. Additionally, the present study divulged a novel motif under basal conditions comprising, -GTGn3GTGn3GTG- where, Hsf1 displays strong occupancy at significant number of sites on several promoters distinct from the heat induced motif. Hence, by binding to and regulating major chaperones, stress responsive genes and drug resistance regulators, Hsf1 is imperative in regulating various cellular machineries. The current study provides a framework for understanding novel aspects of how Hsf1 coordinates diverse cellular functions.