Pleuropulmonary blastoma (PPB) and other DICER1-associated high-grade malignancies are morphologically, genetically and epigenetically related – A comparative study of 4 PPBs and 6 sarcomas

DICER1-mutated rhabdomyosarcoma of the ovary with teratoid features

DICER1-mutated rhabdomyosarcoma is a rare, emerging entity with a predilection for the gynecologic and genitourinary tracts. We report here a case of DICER1-mutated rhabdomyosarcoma of the ovary in a 14 years old girl which displayed interspersed mature teratoid glands, neuroectodermal rosettes and immature blastematous-like tubes. Morphologically the sarcomatous component predominated, corresponding to a high grade spindle cell rhabdomyosarcoma with botryoid features. Islets of cartilage were present. The sarcomatous proliferation encased the teratoid glands, forming cambium layer-like arrangements. The sarcoma cells were Myogenin and MYOD1 positive, the neuroectodermal rosettes expressed SALL4 along with cytokeratins and EMA and were negative for Inhibin; immature blastematous-like tubes were negative for SALL4 and Inhibin. Whole RNA- and targeted DNA-sequencing revealed two DICER1 mutations in exon 26: c.5113G>A: p.(Glu1705Lys) and exon 12: c.1642C>T: p.(Gln548X). The sarcomatous component harbored a complex genetic profile while the teratoid component was diploid, none of the above displayed abnormality of 12p. DICER1-mutated sarcomas display pathological features similar to embryonal rhabdomyosarcomas, botryoid type. They also display heterogeneous features combining cartilage foci, teratoid mature glands, immature blastematous-like tubes and/or neuroectodermal components. Molecular testing remains necessary to confirm the diagnosis. Further studies need to clarify the nosology of DICER1-mutated sarcomas and devise specific therapeutic strategies.

Type II pleuropulmonary blastoma mistaken for rhabdomyosarcoma: A case report

INTRODUCTION

Pleuropulmonary blastoma (PPB) is rare, representing 0.3 % of all pediatric cancers. PPB is classified into three subtypes and may progress from type I to types II and III, with a worse prognosis. Given its rarity, the diagnosis is frequently challenging.

CASE PRESENTATION

We report an occurrence of PPB in a 3-year-old girl, who presented recurrent pneumopathy. Imaging investigations revealed a large solid lesion in the left hemithorax. Biopsy followed by histological analysis suggested rhabdomyosarcoma. The patient received neoadjuvant chemotherapy before proceeding to complete tumor excision. Surgical exploration revealed that the tumor was primitively related to parietal pleura and lower lobe of left lung. Histopathology of the tumor retained a definitive diagnosis of PPB type II. Postoperative course was uneventful, and a cerebral MRI ruled out brain metastasis. Adjuvant chemotherapy was administered.

DISCUSSION

Clinical expression of PPB is nonspecific and variable. It ranges from a dry cough to respiratory distress. Standard radiography is the first examination to perform and CT is the gold standard for characterization thoracic masses. Surgery and chemotherapy are the pillars of treatment. Indications depend on the tumor type, its extent and its resectability.

CONCLUSION

PPB is an aggressive tumor that occurs only in children. Due to the rarity of PPB, evidence on optimal treatment is still insufficient. Careful follow-up is necessary searching for local recurrence or metastasis.

Genomic characterization of DICER1-associated neoplasms uncovers molecular classes

DICER1 syndrome is a tumor predisposition syndrome that is associated with up to 30 different neoplastic lesions, usually affecting children and adolescents. Here we identify a group of mesenchymal tumors which is highly associated with DICER1 syndrome, and molecularly distinct from other DICER1-associated tumors. This group of DICER1-associated mesenchymal tumors encompasses multiple well-established clinicopathological tumor entities and can be further divided into three clinically meaningful classes designated "low-grade mesenchymal tumor with DICER1 alteration" (LGMT DICER1), "sarcoma with DICER1 alteration" (SARC DICER1), and primary intracranial sarcoma with DICER1 alteration (PIS DICER1). Our study not only provides a combined approach to classify DICER1-associated neoplasms for improved clinical management but also suggests a role for global hypomethylation and other recurrent molecular events in sarcomatous differentiation in mesenchymal tumors with DICER1 alteration. Our results will facilitate future investigations into prognostication and therapeutic approaches for affected patients.

From Malignant Thyroid Teratoma to Thyroblastoma: Evolution of a Newly-recognized DICER1 -associated Malignancy

Thyroblastoma is a novel thyroid malignancy included in the 5th Edition WHO Classification of Endocrine and Neuroendocrine Tumours. The majority of tumors now classified as thyroblastoma were originally regarded to be malignant thyroid teratomas. However, these neoplasms were recently recognized as a separate entity based on a distinctive constellation of primitive multilineage elements, including immature thyroid epithelium, undifferentiated or rhabdomyoblastic spindle cell proliferations, and neuroepithelial blastema, as well as recurrent DICER1 hotspot mutations. Thyroblastoma is an aggressive tumor that leads to death from disease in ~50% of patients, making it essential to differentiate this entity from a wide range of other thyroid tumors that show overlapping histologic features or DICER1 mutations. This review aims to provide a practical overview of the background, clinicopathologic features, molecular underpinnings, and differential diagnosis of this recently-described and molecularly-defined entity.

Thyroblastoma: A DICER1-associated embryonal neoplasm and fine needle aspiration diagnostic criteria

Thyroblastoma is a rare, aggressive embryonal thyroid neoplasm associated with DICER1 mutation. It usually presents as a rapidly growing thyroid mass diffusely infiltrating the thyroid lobes and extending into perithyroidal tissue. Most thyroblastomas were initially diagnosed as malignant teratoma or carcinosarcoma. The cytologic features of thyroblastoma have not been well documented. Here, we present the cytological findings of a case of thyroblastoma in a 19-year-old female with a dominant solid left thyroid nodule. A fine needle aspiration biopsy of the mass revealed a highly cellular aspirate composed of crowded, atypical, high nuclear to cytoplasmic ratio epithelial cells, arranged in a variety of architectural patterns including rosette-like microfollicular, solid, and morular. In addition, the background contains a minor population of atypical mesenchymal cells. The cytologic differential diagnosis of thyroblastoma includes primary thyroid neoplasms such as adenomatous nodule, follicular adenoma, follicular carcinoma, and poorly differentiated thyroid carcinoma as well as metastatic carcinoma.