The persistence of cancer cells resistant to therapy remains a major clinical challenge. In triple-negative breast cancer, resistance to chemotherapy results in the highest recurrence risk among ...breast cancer subtypes. The drug-tolerant state seems largely defined by nongenetic features, but the underlying mechanisms are poorly understood. Here, by monitoring epigenomes, transcriptomes and lineages with single-cell resolution, we show that the repressive histone mark H3K27me3 (trimethylation of histone H3 at lysine 27) regulates cell fate at the onset of chemotherapy. We report that a persister expression program is primed with both H3K4me3 (trimethylation of histone H3 at lysine 4) and H3K27me3 in unchallenged cells, with H3K27me3 being the lock to its transcriptional activation. We further demonstrate that depleting H3K27me3 enhances the potential of cancer cells to tolerate chemotherapy. Conversely, preventing H3K27me3 demethylation simultaneously to chemotherapy inhibits the transition to a drug-tolerant state, and delays tumor recurrence in vivo. Our results highlight how chromatin landscapes shape the potential of cancer cells to respond to initial therapy.
The diagnosis, histomolecular classes of breast cancers (luminal A, luminal B, HER2‐enriched, and basal‐like), and accurate prediction of prognosis are commonly determined using morphological and ...phenotypical analyses in clinical practice worldwide. Therapeutic strategies are mostly based on the disease stage and molecular subclasses of breast cancer. Targeted therapies, such as anti‐HER2s, poly‐ADP ribose polymerase inhibitors or, to a lesser extent, phosphatidylinositol 3 kinase inhibitors, have substantially improved breast cancer patient prognosis over the past decades. Human epidermal growth factor receptor 2 (HER2) overexpression is widely determined based on immunohistochemistry, while next‐generation sequencing (NGS) is currently employed to assess the presence of molecular alterations, including breast cancer gene 1 (BRCA1) and 2 or phosphatidylinositol‐4,5‐bisphosphate 3‐kinase catalytic subunit alpha (PIK3CA) mutations, which are targets of these new approved therapies. In addition, next‐generation sequencing (NGS) can aid the pathologist in challenging situations, such as a diagnostic workup for a metastatic carcinoma in lymph nodes of unknown origin, differential diagnosis of spindle cell tumourtumor in the breast between metaplastic carcinoma, malignant PT and sarcoma, o, as well as determining relatedness between primary breast cancers and recurrences. NGS offers a powerful tool that enables the pathologist to combine morphological analyses together with molecular alterations in challenging diagnostic situations.
Aims
High‐grade metaplastic breast carcinoma (HG‐MBC) is a rare subtype of invasive breast carcinoma, mostly triple‐negative. Metaplastic carcinomas are less responsive to neoadjuvant chemotherapy ...and are associated with a worse outcome than invasive carcinomas of no special type.
Methods
Clinicopathological characteristics and immunophenotype were retrospectively assessed in a series of 65 patients diagnosed with HG‐MBC between 2005 and 2017 at the Curie Institute (antibody panel: oestrogen receptor ER, progesterone receptor PR, androgen receptor AR, human epidermal growth factor receptor 2 HER2, programmed death ligand‐1 PD‐L1, and trophoblast cell surface antigen 2 TROP2).
Results
The median age at diagnosis was 59.5 years. Six (9%) patients had metastatic disease at diagnosis. Among the nonmetastatic patients receiving neoadjuvant therapy, 26% (5/19) achieved pathological complete response. Most tumours were pT1/pT2 (77%) and 12% were pN+. Histological subtypes (mixed, squamous, mesenchymal, and spindle cell) were 40%, 35.5%, 15.5%, and 9%, respectively. Tumour‐infiltrating lymphocytes were low or moderate except when squamous differentiation was present. Most tumours were triple‐negative (92%). AR and TROP2 were positive in 34% and 85% of the cases, respectively. PD‐L1 was positive in tumour cells in 18% (cutoff: 1% of positive tumour cells) of the cases and in tumour‐infiltrating immune cells in 40% (cutoff: 1% of tumour area) of the cases. Notably, spindle cell and mesenchymal metaplastic breast carcinomas were mostly PDL1‐negative. Lastly, 21 (32.3%) cases were HER2‐low, all being HER2 1+, with no HER2 2+.
Conclusion
Metaplastic breast carcinoma could benefit from tailored therapeutic strategies adapted to the phenotypic specificities of histological subtypes.
Representative immunostaining examples of androgen receptor (A & B), trophoblast cell surface antigen 2 (C & D), and programmed death ligand‐1 (E & F) expression in metaplastic breast carcinoma. Focal nuclear expression of androgen receptor in mesenchymal (A) and squamous (B) component of high‐grade metaplastic breast carcinoma (HG‐MBC). (C) Example of trophoblast cell surface antigen 2 (Trop2) cytoplasmic expression in a squamous component of HG‐MBC. (D) Strong, diffuse, and membranous staining of Trop2, in a squamous component. (E) Example of programmed death ligant‐1 (PD‐L1) expression in tumour cells: cytoplasmic heterogeneous staining of a squamous component. (F) Example of immune cells staining with PD‐L1‐antibody in a squamous component.
Aims
Malignant tumours of the lacrimal apparatus are rare and frequently show a poor prognosis, with no clear therapeutic standards. Characterisation of the genetic landscape of these rare tumours is ...sparse, and therefore therapeutics generally follow those of their common salivary gland counterparts. To further clarify the pathophysiology and discover potential therapeutic targets, we investigated the genetic landscape of eight tumours of the lacrimal apparatus.
Methods and results
DNA and RNA sequencing were performed to identify genetic mutations and gene fusions. Immunohistochemistry, fluorescence
in‐situ
hybridisation and reverse transcription–polymerase chain reaction followed by Sanger sequencing were performed to confirm the identified molecular alterations. Genetic alterations were detected in six tumours. Among five adenoid cystic carcinomas (ACC), four had confirmed alterations of
MYB
or
MYBL1
genes, including a
MYB
::
NFIB
fusion, a
MYBL1
::
NFIB
fusion, a
MYB
amplification and a novel
NFIB
::
THSD7B
fusion. Mutations in genes encoding epigenetic modifiers, as well as
NOTCH1
,
FGFR2
and
ATM
mutations, were also identified in ACCs. A carcinoma ex pleomorphic adenoma showed
TP53
and
CIC
mutations and an amplification of
ERBB2
. A transitional cell carcinoma was associated with HPV16 infection. No genetic alteration was found for one adenocarcinoma, not otherwise specified.
Conclusions
Our study highlights the variety of molecular alterations associated with lacrimal system tumours and emphasises the importance of molecular testing in these tumours, which can reveal potentially targetable mutations. Our results also reinforce the hypothesis of a common physiopathology of all ACCs, regardless of their primary location.
Aims
Low‐grade adenosquamous carcinoma of the breast (LGASC) is a rare variant of metaplastic carcinoma characterised by a favourable outcome and histologically composed of glandular and squamous ...elements in a spindle cell background typically associated with a lymphocytic stromal reaction. Because of its rarity, the immunophenotypic and genetic profile of LGASC has not been sufficiently characterised. The aim of this study was to gain insights into the molecular and phenotypic characteristics of LGASC.
Methods and results
We reviewed the clinical and morphological features and detailed the immunohistochemical characteristics of a retrospective series of 13 LGASCs. Targeted sequencing of 50 genes was performed in 10 of 13 cases. Identified mutations were further assessed by Sanger sequencing in a validation series of 11 additional cases. All tumours showed a triple‐negative immunophenotype, expressed ‘basal’ keratins, showed variable levels of epidermal growth factor receptor expression, and did not express androgen receptor. Sequencing analysis of the screening set of LGASCs revealed a high rate (seven of 10 cases) of PIK3CA mutations, whereas no TP53 mutations were found. All PIK3CA mutations were missense mutations located either in exon 20 (n = 6) or in exon 9 (n = 1). The global PIK3CA mutation rate, including the validation series, was 52% (11 of 21 cases). No disease recurrences were observed. Correction added on 11 June 2018, after first online publication: The percentage of mutation rate was corrected to 52%
Conclusions
Our results indicate that LGASC of the breast is a low‐grade triple‐negative breast cancer that harbours a basal‐like phenotype with no androgen receptor expression, and shows a high rate of PIK3CA mutations but no TP53 mutations.
Triple‐negative breast cancer (TNBC) represents 10% of all breast cancers and is a very heterogeneous disease. Globally, women with TNBC have a poor prognosis, and the development of effective ...targeted therapies remains a real challenge. Patient‐derived xenografts (PDX) are clinically relevant models that have emerged as important tools for the analysis of drug activity and predictive biomarker discovery. The purpose of this work was to analyze the molecular heterogeneity of a large panel of TNBC PDX (n = 61) in order to test targeted therapies and identify biomarkers of response. At the gene expression level, TNBC PDX represent all of the various TNBC subtypes identified by the Lehmann classification except for immunomodulatory subtype, which is underrepresented in PDX. NGS and copy number data showed a similar diversity of significantly mutated gene and somatic copy number alteration in PDX and the Cancer Genome Atlas TNBC patients. The genes most commonly altered were TP53 and oncogenes and tumor suppressors of the PI3K/AKT/mTOR and MAPK pathways. PDX showed similar morphology and immunohistochemistry markers to those of the original tumors. Efficacy experiments with PI3K and MAPK inhibitor monotherapy or combination therapy showed an antitumor activity in PDX carrying genomic mutations of PIK3CA and NRAS genes. TNBC PDX reproduce the molecular heterogeneity of TNBC patients. This large collection of PDX is a clinically relevant platform for drug testing, biomarker discovery and translational research.
What's new?
Triple‐negative breast cancer (TNBC) is a highly heterogeneous disease in terms of molecular profile, histological features, clinical behavior, and drug response. Several clinical trials have been conducted for targeted therapies, but only in unselected TNBC patients, with disappointing results. This study shows that patient‐derived xenografts (PDX) reproduce the molecular heterogeneity of TNBC. The presented genomic analysis identifies several interesting targetable drivers, particularly in the PI3K and MAPK pathways. PDX models provide a unique opportunity to test various treatments on individual tumors: already, two specific inhibitors (dual PI3K/mTOR and MEK inhibitor) and their combination are providing encouraging results.
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