An isolated childhood myeloid sarcoma with germline MSH6 mutation-a case report

Abstract

Myeloid sarcoma (MS) is a type of malignant tumor that originates in the bone marrow. This study reports on the treatment of an 11-year-old Uygur girl with a 15-day history of fever and paroxysmal cough, accompanied by right hip pain. During treatment, fatigue and anemia developed, physical strength decreased, and a few petechiae were seen in the lower extremities. Multiple enlarged lymph nodes were palpable in the neck, with slight congestion in the pharynx. Routine blood screening showed three major myeloid lineage abnormalities. Pathological examination revealed the presence of CD10 (-), CD99 (+), CD20 (+), CD3 (-), CD117 (weak+), CD34 (unclear location), TdT (-), Pax5 (-), Ki-67 (50%+), MPO (-), and CD43 (+). The patient was eventually diagnosed with isolated MS. After chemotherapy, no small particles were observed in bone marrow morphology. Complete remission was confirmed by flow cytometric detection of minimal residual disease. Genomic DNA was subjected to targeted sequencing of 236 gene panels to detect somatic mutations and the MSH6 c.3953_3954insAA p.R1318fs germline mutation. Unfortunately, the patient was subsequently lost to follow-up. To our knowledge, an MSH6 germline mutation had not previously been reported in children with MS, and we speculated that an MSH6 germline mutation led to genomic instability, triggering a somatic mutation in multiple genes and ultimately led to the development of MS in this patient. It is suggested that rare base abnormalities may be involved in the development of isolated myeloid sarcomas (IMS).

Keywords: Isolated myeloid sarcoma (IMS); MSH6; case report; chemotherapy; somatic mutations.

Figure 1

Immunohistochemical staining of tumor tissues (original magnification ×200). (A) CD99 (+); (B) CD20 (+); (C) CD117 (+); (D) CD34 (+); (E) Ki-67 (+); (F) CD43 (+).

Figure 2

Myeloid sarcoma involving the head mass of an 11-year-old girl. (A) Low-power view showing the infiltrative and destructive pattern of growth of malignant cells (hematoxylin and eosin, original magnification ×200); (B) detection of measurable residual disease by multicolor flow cytometry of bone marrow.

Figure 3

Comparison of the protein conformation of the wild-type MSH6 and mutated-type MSH6 predicted by SWISS-MODEL Interactive Workspace. (A) Protein conformation of Wild-type MSH6; (B) protein conformation of mutated-type MSH6 which occurred in the location of MSH6 c.3953_3954insAA p.R1318fs. The blue arrows indicate the changed location. Blue arrows refer to the location of MSH6 c.3953_3954insAA p.R1318fs.