A pediatric case of osteosarcoma and tuberous sclerosis complex with a novel germline mutation in theTSC2 gene and a somatic mutation in theTP53 gene

To the Editor:

Here, we report on a 12-year-old female who had been diagnosed with tuberous sclerosis complex (TSC) and later developed osteosarcoma. She had hypomelanotic macules on the cheeks and thighs, and magnetic resonance imaging revealed subependymal nodules along the wall of the ependymal lining of the third ventricles. Accordingly, she was diagnosed with TSC. At the age of 6 years, she developed angiofibromatosis of the face, renal angiomyolipoma, and subependymal giant cell astrocytoma (SEGA).
When she was 12, she presented with pain and swelling in the left leg. Magnetic resonance imaging showed a well-circumscribed tumor mass located in the left femoral shaft and distal. Needle biopsy of the left distal femur revealed tumors composed of spindle or polygonal cells and sparse osteoclastic giant cells with atypia producing an osteoid matrix (Figure 1A). Accordingly, she was diagnosed with osteosarcoma of the left femur.
Clinical sequencing of osteosarcoma tissue for a panel of cancerrelated genes identified a somatic missense mutation in the TP53 gene and a novel germline mutation in the TSC2 gene. Two pathogenic mutations were identified: a missense mutation in TP53 (c.404G > A encoding p.C135Y) and a 32-bp deletion in TSC2 (c.5045_5068+8del32).1 The latter was also found in DNA from the patient’s peripheral blood mononuclear cells, suggesting that it is a germline mutation. The c.5045_5068+8del32 mutation in TSC2 was considered pathogenic because it involved an essential splice site of intron 40, although this hasneverbeenreportedinanydatabase.2 Toconfirmthis,weextracted RNAs from the patient’s peripheral blood sample and performed cDNA direct sequencing. We designed primers that combined to form an exon–exon junction; only one extra band appeared in the patient lane, and the result included almost the entire intron 40 sequence, excluding an 8-bp deletion (Figure S1A). A 24-bp deletion in exon 39 and a 98-bp insertion between exons 39 and 40 had occurred, and these caused a frameshift in the mRNA (Figure S1B). The stop codon does not emerge until 3′UTR. Thus, we predict that it is not a target for nonsense-mediated RNA decay, and an abnormal protein would be produced.
Interestingly, immunohistochemical analysis of the osteosarcoma revealed that S6, a downstream target of mTOR present in both tumor and non-tumor cells (Figure 1B),3 was diffusely phosphorylated in the tumor cells (Figure 1C). This is the first reported detection of a germline TSC2 mutation and somatic TP53 mutation in osteosarcoma with tuberous sclerosis. In a recent study, pathway analysis and a comparative oncology approach converged on the PIK3/AKT/mTOR pathway as a central vulnerability for therapeutic exploitation in osteosarcoma.4
Of note, our patient exhibited surprising sensitivity to chemotherapy, resulting in complete remission of the disease. Based on previous reports regarding SEGAs,5 our patient started everolimus at a dose of 3 mg/m2 daily as maintenance therapy. Although further studies are required to better elucidate the molecular pathogenesis of osteosarcoma, our case is JR-AB2-011 unique and suggestive of a possible tumorigenesis from altered mTOR pathway and a 2nd hit from TP53.

KEYWORDS
mTOR inhibitor, osteosarcoma, TP53, TSC2, tuberous sclerosis complex

REFERENCES

1. Moriya K, Kaneko MK, Liu X, et al. IDH2 and TP53 mutations are correlated with gliomagenesis in a patient with Maffucci syndrome. Cancer Sci. 2014;105(3):359-362.
2. Dufner Almeida LG, Nanhoe S, Zonta A, et al. Comparison of the functional and structural characteristics of rare TSC2 variants with clinical and genetic findings. Hum Mutat. 2020;41(4):759-773.
3. Tee AR, Fingar DC, Manning BD, Kwiatkowski DJ, Cantley LC, Blenis J. Tuberous sclerosis complex-1 and -2 gene products function together to inhibit mammalian target of rapamycin (mTOR)-mediated downstream signaling. Proc Natl Acad Sci U S A. 2002;99(21):13571-13576.
4. Perry JA, Kiezun A, Tonzi P, et al. Complementary genomic approaches highlight the PI3K/mTOR pathway as a common vulnerability in osteosarcoma. Proc Natl Acad Sci U S A. 2014;111(51):E5564-E5573.
5. Franz DN, Agricola K, Mays M, et al. Everolimus for subependymal giant cell astrocytoma: 5-year final analysis. Ann Neurol. 2015;78(6):929-938.