Tumor samples are conserved in clinical practice in formalin-fixed paraffin-embedded (FFPE) blocks. Formalin fixation chemically alters nucleic acids, rendering transcriptomic analysis challenging. RNA-sequencing is usually performed on tumor bulk, without distinction of cell subtypes or location. Here we describe the development of a robust method for RNA extraction and exome-capture RNA-sequencing of lasercapture microdissected tumor cells (TC) and stromal immune cells (TIL) based on their morphology. We applied this method on 7 tumor samples (surgical or core needle biopsy) of triple-negative breast cancer (TNBC) stored in FFPE blocks over 3-10 years.Unsupervised clustering and principal component analysis showed a clear separation between gene-expression profile of TIL and TC. TIL were enriched in markers of B cells (CD79B, PAX5 and BLNK ) and T cells (CD2, CD3D and CD8B) whereas tumor cells expressed epithelial markers (EPCAM, MUC1 and KRT8). Microenvironment cell populations-counter (MCP)-counter deconvolution showed an enrichment in adaptive immune cell signatures in microdissected TIL. Transcripts of immune checkpoints were differentially expressed in TIL and TC. We further validated our results by qRT-PCR and multispectral immunohistochemistry. In conclusion, we showed that combining laser-capture microdissection and RNA-sequencing on archived FFPE blocks is feasible and allows spatial transcriptional characterization of tumor microenvironment.
BRCA1 and BRCA2 play a central role in DNA repair and their germline pathogenic variants (gBRCA) confer a high risk for developing breast and ovarian cancer. Standard chemotherapy regimens for these cancers include DNA-damaging agents. We hypothesized that gBRCA carriers might be at higher risk of developing chemotherapy-related hematologic toxicity and therapy-related myeloid neoplasms (t-MN). We conducted a retrospective study of women newly diagnosed with invasive breast or ovarian cancer who were screened for gBRCA1/gBRCA2 at Geneva University Hospitals. All patients were treated with (neo-)adjuvant chemotherapy. We evaluated acute hematologic toxicities by analyzing the occurrence of febrile neutropenia and severe neutropenia (grade 4) at day 7–14 of the first cycle of chemotherapy and G-CSF use during the entire chemotherapy regimen. Characteristics of t-MN were collected. We reviewed medical records from 447 patients: 58 gBRCA1 and 40 gBRCA2 carriers and 349 non-carriers. gBRCA1 carriers were at higher risk of developing severe neutropenia (32% vs. 14.5%, p = 0.007; OR = 3.3, 95% CI [1.6-7], p = 0.001) and of requiring G-CSF for secondary prophylaxis (58.3% vs. 38.2%, p = 0.011; OR = 2.5, 95% CI [1.4–4.8], p = 0.004). gBRCA2 carriers did not show increased acute hematologic toxicities. t-MN were observed in 2 patients (1 gBRCA1 and one non-carrier). Our results suggested an increased acute hematologic toxicity upon exposure to chemotherapy for breast and ovarian cancer among gBRCA1 but not gBRCA2 carriers. A deeper characterization of t-MN is warranted with the recent development of PARP inhibitors in frontline therapy in gBRCA breast and ovarian cancer.
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