Dual loss of the SWI/SNF complex ATPases SMARCA4/BRG1 and SMARCA2/BRM is highly sensitive and specific for small cell carcinoma of the ovary, hypercalcaemic type

SMARCA4 and SMARCA2 deficiency in non-small cell lung cancer: immunohistochemical survey of 316 consecutive specimens

The chromatin remodeling switch sucrose nonfermentable (SWI/SNF) complex has been increasingly implicated in the pathogenesis and dedifferentiation of neoplasms from several organs with prognostic and potential therapeutic implications. We herein investigated the expression of the SWI/SNF complex catalytic subunits SMARCA4 (BRG1) and SMARCA2 (BRM) in 316 consecutive non-small cell lung cancer (NSCLC) specimens on tissue microarrays (171 adenocarcinomas [ADCAs], 130 squamous cell carcinomas [SCCs], 9 adenosquamous carcinomas, and 6 large cell carcinomas) excluding undifferentiated/giant cell or rhabdoid carcinomas. Complete loss of SMARCA4 was observed in 8 (5.5%) of 146 evaluable pulmonary ADCAs and 6 (5.2%) of 115 evaluable pulmonary SCCs, whereas 9 (6.4%) of 140 ADCAs and 2 (1.7%) of 117 SCCs showed SMARCA2 loss. Two of 6 large cell carcinomas were SMARCA2 deficient. Concurrent loss of both markers was observed in 4 cases (2 ADCAs and 2 SCCs). Of 15 ADCAs with loss of either or both markers, 12 (80%) were TTF1 negative. In conclusion, SMARCA4 and SMARCA2 deficiency is observed in 5.1% and 4.8% of NSCLC, respectively. SMARCB1 expression was intact in all cases. The presence of differentiated histology (glandular or squamous) is a novel aspect among SWI/SNF-deficient carcinomas which in other organs generally are associated with undifferentiated/rhabdoid morphology. The predominance of TTF1 negativity among SWI/SNF-deficient pulmonary ADCA (80%) underlines the need to include these 2 markers in the evaluation of TTF1-negative ADCA of putative pulmonary origin. Given the recently documented potential of SMARCA4 loss as a predictor of chemosensitivity to platinum-based chemotherapy in NSCLC, recognition of the clinicopathological features of SMARCA4-deficient NSCLC in routine surgical pathology practice is recommended.

SCCOHT tumors acquire chemoresistance and protection by interacting mesenchymal stroma/stem cells within the tumor microenvironment

Chemotherapeutic drug testing of SCCOHT-1 and BIN-67 tumor cells revealed synergistic growth-inhibition of >95% in vitro with a combination of foretinib and FK228. Application of this drug combination in vivo in NODscid mice-induced SCCOHT-1GFP tumors was associated with ~6-fold reduction in tumor mass within 10 days, whereby synergistic effects of the two compounds remained undetectable compared to previous results with foretinib treatment alone. Histopathologic evaluation revealed a reduced vascularization and a lower amount of proliferating cells in the treated tumors. Surprisingly, a simultaneous significant accumulation of extracellular matrix structures with positive elastin-van Gieson staining was observed following foretinib/FK228 exposure. Expression analysis of treated animal tumors exhibited various changes including increased mouse transcript levels of elastin, laminin, and fibronectin. In parallel, markers for mesenchymal stroma/stem cells (MSC) including CD73 and CD90 were detectable in all mouse tumors suggesting a possible involvement of these cells in extracellular matrix restructure. Indeed, incubation of MSC with FK228 or foretinib/FK228 demonstrated morphologic alterations and enhanced expression of laminin and fibronectin. Moreover, a co-culture of MSC with lentiviral-labeled SCCOHT-1GFP cells contributed to protection of the tumor cells against FK228-mediated cytotoxicity. Furthermore, explant cultures of SCCOHT-1GFP-induced tumors acquired an increased resistance to FK228 and a combination of foretinib/FK228 in contrast to foretinib alone. Together, these data suggested that FK228-mediated extracellular matrix protein expression by MSC contributes to increased protection and enhanced resistance of SCCOHT tumors which could represent a more general mechanism of MSC during drug-induced alterations of a tumor microenvironment.

Lifting Up the HAT: Synthetic Lethal Screening Reveals a Novel Vulnerability at the CBP-p300 Axis

Cancer genotype-specific synthetic lethal vulnerabilities represent promising therapeutic targets. In this issue of Cancer Discovery, Ogiwara and colleagues uncover a synthetic lethal relationship between two histone acetyl transferase paralogs, CBP and p300, highlighting that cancer cells deficient in CBP are uniquely sensitized to genetic and chemical inhibition of p300.

Genomic/Epigenomic Alterations in Ovarian Carcinoma: Translational Insight into Clinical Practice

Ovarian carcinoma is the most lethal gynecological malignancy worldwide. Recent advance in genomic/epigenomic researches will impact on our prevention, detection and intervention on ovarian carcinoma. Detection of germline mutations in BRCA1/BRCA2, mismatch repair genes, and other genes in the homologous recombination/DNA repair pathway propelled the genetic surveillance of most hereditary ovarian carcinomas. Germline or somatic mutations in SMARCA4 in familial and sporadic small cell carcinoma of the ovary, hypercalcemia type, lead to our recognition on this rare aggressive tumor as a new entity of the atypical teratoma/rhaboid tumor family. Genome-wide association studies have identified many genetic variants that will contribute to the evaluation of ovarian carcinoma risk and prognostic prediction. Whole exome sequencing and whole genome sequencing discovered rare mutations in other drive mutations except p53, but demonstrated the presence of high genomic heterogeneity and adaptability in the genetic evolution of high grade ovarian serous carcinomas that occurs in cancer progression and chemotherapy. Gene mutations, copy number aberrations and DNA methylations provided promising biomarkers for the detection, diagnosis, prognosis, therapy response and targets of ovarian cancer. These findings underscore the necessity to translate these potential biomarkers into clinical practice.

Loss of switch/sucrose non-fermenting complex protein expression is associated with dedifferentiation in endometrial carcinomas

Dedifferentiated endometrial carcinoma is an aggressive type of endometrial cancer that contains a mix of low-grade endometrioid and undifferentiated carcinoma components. We performed targeted sequencing of eight dedifferentiated carcinomas and identified somatic frameshift/nonsense mutations in SMARCA4, a core ATPase of the switch/sucrose non-fermenting (SWI/SNF) complex, in the undifferentiated components of four tumors. Immunohistochemical analysis confirmed the loss of SMARCA4 in the undifferentiated component of these four SMARCA4-mutated cases, whereas the corresponding low-grade endometrioid component showed retained SMARCA4 expression. An expanded survey of other members of the SWI/SNF complex showed SMARCB1 loss in the undifferentiated component of two SMARCA4-intact tumors, and all SMARCA4- or SMARCB1-deficient tumors showed concomitant loss of expression of SMARCA2. We subsequently examined the expression of SMARCA2, SMARCA4, and SMARCB1 in an additional set of 22 centrally reviewed dedifferentiated carcinomas and 31 grade 3 endometrioid carcinomas. Combining the results from the index and the expansion set, 15 of 30 (50%) of the dedifferentiated carcinomas examined showed either concurrent SMARCA4 and SMARCA2 loss (37%) or concurrent SMARCB1 and SMARCA2 loss (13%) in the undifferentiated component. The loss of SMARCA4 or SMARCB1 was mutually exclusive. All 31 grade 3 endometrioid carcinomas showed intact expression of these core SWI/SNF proteins. The majority (73%) of the SMARCA4/SMARCA2-deficient and half of SMARCB1/SMARCA2-deficient undifferentiated component developed in a mismatch repair-deficient molecular context. The observed spatial association between SWI/SNF protein loss and histologic dedifferentiation suggests that inactivation of these core SWI/SNF proteins may contribute to the development of dedifferentiated endometrial carcinoma.