Convergent Germline Mutations in TP53 and BRCA1 Driving Multi-lineage Metachronous Malignancies: A Familial Case of Overlapping Li-Fraumeni and Hereditary Breast and Ovarian Cancer Syndromes in Siblings

INTRODUCTION

Hereditary cancer syndromes are typically characterised by single-gene mutations; however, the coexistence of multiple high-penetrance germline mutations can dramatically expand the spectrum and tempo of oncogenesis. We present a remarkable case of overlapping hereditary cancer syndromes – Li-Fraumeni syndrome (LFS) and hereditary breast and ovarian cancer (HBOC) – in a single patient harbouring germline pathogenic variants in TP53 and BRCA1. This synergistic mutational constellation disrupted distinct yet interrelated tumour suppressor pathways governing genomic surveillance, homologous recombination (HR) repair and cell cycle control, ultimately predisposing the patient to a broad lineage of malignancies across time.^[1]

The patient’s clinical trajectory began with hormone receptor-negative breast cancer, later recurring locally as hormone receptor–positive, human epidermal growth factor receptor 2 (HER2) (2+) disease. This was followed by high-grade serous ovarian carcinoma, papillary thyroid carcinoma harbouring a somatic BRAF V600E mutation and retroperitoneal leiomyosarcoma (LMS) with RB1 and later FGFR3 alterations. The disease course culminated in therapy-related acute myeloid leukaemia (t-AML) driven by an IDH2 mutation [Figure 1]. Notably, the synchronous presentation of epithelial and mesenchymal tumours – papillary thyroid carcinoma and LMS – further underscores the extensive tumour lineage susceptibility conferred by compound germline defects.

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Figure 1: Chronological evolution of multiple malignancies with germline TP53 and BRCA1 in the proband patient (SB), CBC: Complete blood count, PBS: Peripheral blood smear.

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The sequential emergence of these malignancies exemplifies the classical ‘second-hit’ hypothesis of tumorigenesis – first proposed by Knudson – which posits that both alleles of a tumour suppressor gene must be inactivated for malignant transformation to occur.^[2] In hereditary cancer syndromes, the first hit is typically a germline mutation, while the second hit arises somatically through point mutations, loss of heterozygosity or epigenetic silencing. In this patient, second-hit somatic mutations – including BRAF V600E, RB1, FGFR3 and IDH2 – acted as oncogenic drivers, shaping tumour evolution and progression over time.

In contrast, the patient’s sibling, who harboured only a germline BRCA1 mutation, developed an isolated ovarian malignancy, further supporting the role of multi-locus germline interactions in modulating cancer susceptibility and phenotypic diversity.^[2] This case highlights the imperative for comprehensive germline and somatic multigene profiling in patients presenting with complex, recurrent or lineage-diverse cancers. It also underscores the translational value of identifying targetable somatic mutations within hereditary cancer contexts and advocates for longitudinal genomic surveillance to inform prognosis, targeted therapy and familial counselling.^[3]

CASE SERIES

DISCUSSION

The primary differential included BRCA1-associated HBOC syndrome. However, the appearance of sarcoma and therapy-related haematological malignancy prompted evaluation for LFS. The synchronous presentation of epithelial and mesenchymal tumours along with the familial clustering confirmed dual germline mutation inheritance – TP53 and BRCA1.

This report presents an instructive example of overlapping hereditary cancer syndromes – LFS and HBOC – in a single patient harbouring convergent germline mutations in TP53 (c.743G>A, p.R248Q) and BRCA1 (c.1039delC, p.L347fsX27). Convergent germline mutations refer to the presence of two or more inherited (germline) genetic mutations in the same individual that affect different but critical tumour suppressor or DNA repair pathways and together increase the risk of cancer development far more than each would alone. These mutations disrupted two cardinal tumour suppressor axes: The p53-mediated DNA damage response and BRCA1-driven HR repair, predisposing the patient to a cascade of metachronous and synchronous malignancies including breast cancer, high-grade serous ovarian carcinoma, papillary thyroid carcinoma, retroperitoneal LMS and t-AML.^[1-3]

TP53 encodes the p53 transcription factor, often referred to as the ‘guardian of the genome’, due to its role in activating DNA repair, cell cycle arrest and apoptosis in response to genotoxic stress.^[4] Germline TP53 mutations underlie LFS and confer a high lifetime risk of diverse early-onset cancers.^[5] The R248Q mutation observed here is a well-characterised dominant-negative hotspot variant that impairs p53’s DNA-binding capacity and transactivation of downstream effectors such as p21, BAX and GADD45, thereby promoting unchecked proliferation of damaged cells.^[6,7]

BRCA1, a hallmark gene of the HBOC spectrum, governs HR repair of DNA double-strand breaks.^[8] The c.1039delC mutation in exon 11 results in a frameshift and premature protein truncation (p.L347fsX27), rendering BRCA1 nonfunctional. Loss of BRCA1 activity shifts DNA repair to error-prone non-homologous end-joining, culminating in chromosomal rearrangements and oncogenesis.^[9,10] The cooccurrence of TP53 and BRCA1 loss creates a synergistically mutagenic microenvironment characterised by defective damage recognition, faulty repair and impaired apoptosis.^[11]

Over the disease trajectory, the patient accumulated distinct somatic mutations, consistent with the classical ‘second-hit’ hypothesis.^[12] In papillary thyroid carcinoma, the BRAF V600E mutation activated the MAPK/ERK cascade, driving mitogenic signalling and cellular transformation.^[13,14] This mutation is among the most common oncogenic events in sporadic thyroid cancers and reflects clonal selection within a genomically unstable landscape.

In the retroperitoneal LMS, a somatic mutation in RB1 was identified. The RB1 gene encodes the retinoblastoma protein, a key tumour suppressor that regulates the G1/S transition in the cell cycle by inhibiting E2F transcription factors. Loss of RB1 function leads to unchecked cellular proliferation through constitutive E2F activation.^[15] Somatic RB1 alterations are among the most frequently reported mutations in LMSs, present in up to 80–90% of cases in some genomic series.^[16] RB1 inactivation in LMS can occur through diverse mechanisms including point mutations, homozygous deletions, promoter methylation or structural rearrangements, often in conjunction with TP53 mutations, suggesting a cooperative oncogenic effect.^[17] The dual disruption of RB1 and TP53 impairs both the G1/S checkpoint and DNA damage-induced apoptosis, driving chromosomal instability, aggressive tumour behaviour and resistance to therapy.^[18] In addition, RB1 loss in LMS is associated with increased genomic complexity and may correlate with poorer prognosis and limited response to standard cytotoxic regimens.^[19] The presence of a somatic RB1 mutation in our case, against the backdrop of germline TP53 loss, likely provided a proliferative advantage, facilitating sarcomagenesis and metastatic progression.

Subsequently, a somatic FGFR3 p.R397H mutation was identified in liver metastases of the LMS. FGFR3, a receptor tyrosine kinase, plays a role in the PI3K/AKT and MAPK signalling pathways. Activating mutations in FGFR3 are oncogenic and have been implicated in both urothelial and mesenchymal tumours and may represent a potential therapeutic target.^[20]

The final malignancy, t-AML, harboured somatic IDH2 R172K and R172S mutations. These gain-of-function mutations result in the accumulation of the oncometabolite 2-hydroxyglutarate, which interferes with histone and DNA demethylation, ultimately blocking haematopoietic differentiation.^[21,22] The presence of IDH2 mutations in t-AML arising in the context of an underlying germline TP53 mutation portends a poor prognosis and limited response to standard chemotherapy.^[23]

By contrast, the patient’s sister – who harboured only the BRCA1 germline mutation – developed an isolated ovarian carcinoma without subsequent malignancies. This intra-familial phenotypic divergence highlights the dominant role of TP53 in expanding tumour spectra, increasing cancer multiplicity and accelerating oncogenic tempo.^[24]

Overall, this case illustrates the molecular architecture of hereditary cancer syndromes driven by convergent germline mutations and reinforced by somatic evolution. The sequential acquisition of BRAF, RB1, FGFR3 and IDH2 mutations exemplifies clonal selection within a permissive mutator phenotype. This trajectory validates the utility of serial molecular profiling, not only for prognostication and therapeutic targeting, but also for familial risk assessment.

CONCLUSION

This rare case underscores the catastrophic synergy between germline TP53 and BRCA1 mutations, which conspired to produce a spectrum of lineage-diverse malignancies through a multistep oncogenic process. The subsequent acquisition of somatic mutations – BRAF V600E, RB1, FGFR3 and IDH2 – demonstrates classical clonal evolution through secondary hits that exploit the foundational genomic instability. Importantly, the phenotypic contrast with her BRCA1-only sibling reinforces the determinant role of TP53 in shaping cancer risk, tissue tropism and tempo. These findings advocate for comprehensive germline and somatic mutation profiling in patients with unusual cancer histories. They also exemplify the value of precision oncology approaches in dissecting the molecular underpinnings of hereditary cancer and tailoring surveillance and therapy accordingly.