BRCA2 Loss-of-Function and High Sensitivity to Cisplatin-Based Chemotherapy in a Patient With a Pleomorphic Soft Tissue Sarcoma: Effect of Genomic Medicine

Soft tissue sarcomas (STS) represent a heterogeneous group of cancers with many histologic subtypes. In localized tumors, large surgical resection is the standard treatment. A multimodal treatment with radiotherapy or anthracycline-based chemotherapy or both is discussed in highly-specialized multidisciplinary staff, especially for large-size or high-grade sarcomas. Most cases of sarcomas are considered as sporadic. To date, few germline mutations were described to predispose to sarcomas. They target tumor suppressor genes, such as TP53 in Li-Fraumeni syndrome and RB1 in hereditary retinoblastoma. Tumor genome sequencing programs identified recurrent somatic translocations leading to tumor-driver gene fusions in specific types of sarcomas. However, few point mutation driver events were identified. Increased translational and clinical research in sarcoma patients aims to develop targeted therapies. Nevertheless, in contrast to gastro intestinal stromal tumors (GISTs), pleomorphic sarcomas remain an orphan disease without targetable genetic abnormalities.

Heterozygous germline mutations in the tumor suppressors BReast-CAncer susceptibility genes 1 (BRCA1) and 2 (BRCA2) predispose to breast and ovarian cancers. Both genes contribute to DNA repair and transcriptional regulation in response to DNA damage. BRCA1 and BRCA2 genes are involved in homologous DNA recombination-mediated reparation of double strand DNA breaks. The BRCA2 protein contains several copies of a 70 amino acids motif called the BRC motif, and these motifs mediate binding to the RAD51 recombinase which functions in DNA repair. Tumors related to BRCA1 or BRCA2 mutations exhibit enhanced sensitivity to cisplatinum-based chemotherapy. Preclinical and clinical data reported sensitivity of BRCA1/2 mutated cancers to platinum agents. Platinum agents generate interstrand and intrastrand DNA adducts that activate DNA damage response and induce DNA repair. In absence of a functional DNA repair system (such as in cases of BRCA1/2 alterations), DNA damages accumulate and trigger cellular death. Therapies targeting homologous DNA recombination, such as poly ADN-ribose polymerase (PARP)-inhibitors have allowed an increase in survival in BRCA1/2-mutated ovarian and breast cancers according to the concept of synthetic lethality. Studies are ongoing to evaluate PARP-inhibitors in patients with other BRCA1/2 mutations-related cancers such as pancreatic and prostate cancers.

Here, we present the case of a patient with a BRCA2 germline mutation who developed a STS with somatic BRCA2 loss-of-heterozygosity (LOH). This case underlies the clinical effect of germline and somatic sequencing in genomic medicine to monitor therapy decision in sarcoma patients.

A 61-year-old woman patient with a known germinal BRCA2 mutation developed a pleomorphic soft tissue sarcoma of the left thigh. She had a familial and personal history of cancer predisposition. Her sister developed an ovarian cancer at 54. The patient developed a breast cancer at 53 and was treated by conservative surgery, anthracyclines-based chemotherapy and radiotherapy. At the age of 54, she underwent prophylactic bilateral ovariectomy because of the identification of a germinal BRCA2 mutation (c.7007 G>C, p.Arg2336Pro: class 5 causal variant). Informed consents to participate and to publish were obtained from the patient.

At diagnosis, the tumor of the left thigh clinically measured 190 × 230 millimeters (mm) with 1 palpable ipsilateral inguinal node. She had a ECOG 1 performance status. Magnetic resonance imaging (MRI) showed a heterogeneous mass of the left quadriceps. This mass had hyposignal on T1-weighted and hypersignal on short T1 inversion recovery-weight with heterogeneous enhancement after intravenous administration of a gadolinium chelate. The mass was 80 × 75 × 180 mm (Figure 1) at the initial MRI. The computed tomography scan confirmed 2 inguinal lymph node metastases without lung metastases. A tumor microbiopsy revealed a grade 3 pleomorphic soft tissue sarcoma according to Federation Nationale des Centres de Lutte Contre le Cancer (FNCLCC) classification. The histologic subtype of sarcoma, the tumor size, the tumor grade and the lymph node involvement were poor prognostic features, whereas PS1 and no distant metastases were good prognostic factors. The tumor was not accessible to conservative surgery and radical surgery with amputation was discussed. BRCA1/2 molecular analysis was performed on a primary tumor sample using targeted next generation sequencing (Ion AmpliSeq Library Kit on Personal Genome Machine System, Thermo Fisher Scientific) as previously described. The known germline pathogenic BRCA2 mutation (c.7007 G>C, p.Arg2336Pro) was found with an 87% variant allele frequency, a typical feature of LOH. LOH was confirmed using CGH-array on the primary tumor sample (OncoScan CNV FFPE Assay, Affymetrix Inc.) (Figure 2). Because of this molecular result, the standard protocol combining doxorubicin and ifosfamide was modified to incorporate cisplatinum. The patient received 1 cycle of doxorubicin: 30 mg/m², day 1 and 2, cisplatin: 50 mg/m², day 1 and 2, ifosfamide: 2.5 g/m² day 1 and 2 and 1 cycle of doxorubicin: 30 mg/m², day 21 and 22 and ifosfamide: 2.5 g/m², day 21 and 22. A very rapid partial response was clinically and radiologically observed following the first treatment cycle (Figure 1). Because of the history of breast cancer treated by anthracyclines, as the cumulative maximum dose of doxorubicin was reached with subclinical cardiologic consequences on ultrasound heart examination, doxorubicin was stopped, and the patient received 1 additional cycle of cisplatin (30 mg/m², day 1, 2 and 3) and etoposide (120 mg/m², day 1, 2 and 3). Each infusion of chemotherapy was complicated by grade IV neutropenia and anemia. MRI and computed tomography scan were performed after completion of 3 chemotherapy cycles. They confirmed a major partial response with tumor shrinkage: the mass decreased from 80 × 75 × 180 mm (at diagnosis) to 41 × 27 × 80 mm. The objective response was a 56% reduction in 1 size and the residual 3D volume was 8% of the initial volume. The ipsilateral inguinal nodes disappeared. This major tumor response allowed to transform the amputation plan into a conservative surgical resection of the primary tumor. Surgery of the primary tumor with ipsilateral lymphadenectomy was performed 1 month after neoadjuvant chemotherapy. The surgery was conservative with a wide excision with negative margins (R0). The postoperative pathologic assessment showed a histologic response with rare viable tumor cells and necrosis, and 2 inguinal lymph nodes with no tumor cells. Radiotherapy was delivered postoperatively to a total dose of 59.4 Grays. After 24 months of follow up, there was no evidence of local or metastatic recurrence.

BRCA1 and BRCA2 germline mutations predispose to breast and ovarian cancers. Prostatic cancers, melanomas and pancreatic adenocarcinomas were also reported with BRCA2 germline mutations.^,  Some observations described BRCA1 and BRCA2 germline mutations in other subtypes of cancers. Parry et al report germline mutations in DNA repair genes in lung adenocarcinomas with notably 7 germline mutations in ATM and 1 in BRCA2.

In case of cancer diagnosis, germline genetic testing decision is currently based on clinical criteria, including age and familial history. Sarcomas are not classically described to belong to the BRCA2 cancer spectrum. However, since the advent of high throughput sequencing, BRCA1 and BRCA2 germline mutations have been identified in patients with sarcomas.^,  Recently, Ballinger et al performed sequencing of 72 genes in blood samples of 1,162 sarcoma probands, regardless of their familial history. They reported an enrichment of pathogenic variations in the BRCA2 gene (3.6%) among sarcoma patients.

Carlo et al found 25 pathogenic mutations in 101 patients with urothelial cancers. Among them, 12 mutations were also in DNA repair genes, including 3 mutations in BRCA1 and 2 in BRCA2. These results and our observation suggest that current clinical criteria may be insufficient to identify all cancer predisposed patients. Thanks to high throughput sequencing, a larger proportion of cancers will be link to germline genetic variations.

The Cancer Genome Atlas^,  revealed 3% of BRCA2 somatic mutations or deletions in sarcomas. In the present case, BRCA2 LOH in the tumor sample suggested that BRCA2 complete loss-of-function (with bi-allelic BRCA2 inactivation) was a driver event in sarcoma genesis. Preclinical and clinical data reported sensitivity of BRCA1/2 mutated cancers to platinum agents. Platinum-based agents are not usually administrated in STS. Owing to the significantly greater primary chemotherapy sensitivity to platinum-based chemotherapy agents in patients with BRCA1/2-altered tumors, the patient received cisplatin chemotherapy. The enhanced tumor response to cisplatin-based chemotherapy illustrates the importance of tumor molecular characterization to drive clinical treatment decisions in cancer patients.

Current developments of targeted therapies may provide new treatment opportunities in cancer patients with specific somatic driver molecular alterations. In case of recurrence, new therapeutic options based on the known germline and somatic BRCA2 alterations should be considered in the patient. PARPs inhibitors have shown efficiency in BRCA1/2-altered tumors. PARPs inhibition compromises base excision repair in response to single-stranded DNA breaks. Cancer cells with BRCA1/2 deficiency are defective in DNA repair by homologous recombination and sensitive to interstrand DNA crosslinking agents, such as cisplatin, carboplatin and PARP inhibitors. Alternative new strategies are developed to target BRCA1/2 deficiency and open new treatment possibilities. Trabectidin was approved for the treatment of patients with advanced STS after failure of anthracyclines and ifosfamide. Trabectedin covalently binds to the minor groove of the DNA double helix and causes the inhibition of the transcription process, which in turn triggers a cascade of events that interfere with DNA repair pathways. Cells deficient in homologous recombination are more sensitive to trabectedin because of the persistence of DNA lesions and increased formation of replication-dependent double-stranded DNA breaks.

This case illustrates the good response to cisplatin in a BRCA2-mutated pleomorphic sarcoma. This observation emphasizes the input of cancer genomic medicine in clinical practice, its importance in guiding treatment decisions, and the increased overlap between constitutional and somatic molecular genetics.