Targeted therapy of advanced parathyroid carcinoma guided by genomic and transcriptomic profiling

Abstract

Parathyroid carcinoma (PC) is an ultra-rare malignancy with a high risk of recurrence after surgery. Tumour-directed systemic treatments for PC are not established. We used whole-genome and RNA sequencing in four patients with advanced PC to identify molecular alterations that could guide clinical management. In two cases, the genomic and transcriptomic profiles provided targets for experimental therapies that resulted in biochemical response and prolonged disease stabilization: (a) immune checkpoint inhibition with pembrolizumab based on high tumour mutational burden and a single-base substitution signature associated with APOBEC (apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like) overactivation; (b) multi-receptor tyrosine kinase inhibition with lenvatinib due to overexpression of FGFR1 (Fibroblast Growth Factor Receptor 1) and RET (Ret Proto-Oncogene) and, (c) later in the course of the disease, PARP (Poly(ADP-Ribose) Polymerase) inhibition with olaparib prompted by signs of defective homologous recombination DNA repair. In addition, our data provided new insights into the molecular landscape of PC with respect to the genome-wide footprints of specific mutational processes and pathogenic germline alterations. These data underscore the potential of comprehensive molecular analyses to improve care for patients with ultra-rare cancers based on insight into disease biology.

Keywords: RNA sequencing; immune checkpoint inhibition; mutational signature; tumour mutational burden; tyrosine kinase inhibition; whole-genome sequencing.

Fig. 1

Genomic landscape of PC. (A) Recurrent (identified in at least two samples) mutations affecting known PC driver genes and germline predisposition genes (from a curated list of 143 established predisposition genes). (B) Absolute contribution of mutational signatures to the overall SNV load in PC patients. Each bar represents the number of SNVs explained by the respective mutational signature in an individual tumour. Error bars represent 95% confidence intervals. SBS1, clock‐like, spontaneous deamination; SBS2 and SBS13, altered APOBEC activity; SBS3, defective HR; SBS18, damage by reactive oxygen species. Of note, SBS18 shows a similar profile as SBS36, which is associated with defective base excision repair due to MUTYH inactivation. In patient PC‐D, who displays SBS18, a pathogenic MUTYH germline mutation was identified. SBS40 is of unknown aetiology, but mutation numbers attributed to this signature are correlated with patient age in some cancer types. (C) Two CNV clusters with loss of chromosome 3q in patients PC‐A, B, and C. TCC, tumour cell content.

Fig. 2

Immunofluorescence microscopic detection of 8‐oxoG in archived tissue specimens. (A, E) Overlay images of DAPI (blue) and 8‐oxoG (green) staining at low magnification (scale bar 400 μm). At higher magnification (scale bar 100 μm), detection of intense nucleolar staining of 8‐oxoG (B, F: DAPI; C, G: 8‐oxoG; D, H: overlay) in the heterozygous MUTYH mutation carrier PC‐D (F–H) but not in a MUTYH‐wildtype specimen from PC‐A (B–D). DAPI, 4′,6‐diamidino‐2‐phenylindole; 8‐oxoG, 8‐oxo‐guanine.

Fig. 3

Kinase expression landscape of PC. (A) mRNA expression of 138 kinases targeted by at least one of 37 FDA‐approved small‐molecule inhibitors in the four PC samples. (B) Ranking of kinase inhibitors by the number of targets expressed in the top 25%. (C) Drug–target matches for kinase inhibitors with at least five overexpressed targets in at least two samples. Note that for PC‐B, which showed both FGFR1 and RET overexpression, only RET was predicted as a lenvatinib target. FDA, United States Food and Drug Administration.

Fig. 4

Biochemical response of patient PC‐B to lenvatinib and olaparib. Tumour progression with parathyroid hormone increased to 436 pg·mL⁻¹ (reference range, 12–68 pg·mL⁻¹) and moderate hypercalcemia (2.8 mmol·L⁻¹; reference range, 2.2–2.5 mmol·L⁻¹) despite cinacalcet treatment was observed. Administration of the TK inhibitor lenvatinib at a dose of 24 mg decreased parathyroid hormone to 113 pg·mL⁻¹ within 3 weeks, and symptomatic hypocalcemia of 1.9 mmol·L⁻¹ with paresthesias and muscle cramps occurred, requiring replacement of calcium citrate and activated vitamin D. Lenvatinib was discontinued because of renal impairment. Five months later, radiologic and biochemical progression occurred. Further molecularly informed treatment with the PARP inhibitor olaparib was started, resulting in disease stabilization as the best response. After 14 months, olaparib was discontinued due to disease progression, and lenvatinib was reintroduced, resulting in another biochemical response. PTH, parathyroid hormone; Ca, calcium.