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    P38 - Pathology - Pathology/Staging (ID 108)

    • Event: WCLC 2020
    • Type: Posters
    • Track: Pathology, Molecular Pathology and Diagnostic Biomarkers
    • Presentations: 1
    • Moderators:
    • Coordinates: 1/28/2021, 00:00 - 00:00, ePoster Hall
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      P38.17 - Pulmonary Small Cell Carcinoma with Rhabdomyoblastic Differentiation: A Previously Unreported Occurrence (ID 3586)

      00:00 - 00:00  |  Presenting Author(s): Jasper Johar

      • Abstract
      • Slides

      Introduction

      While various types of specific heterologous mesenchymal differentiation occur in pulmonary carcinoma, rhabdomyoblastic differentiation has not been previously reported in association with pulmonary small cell carcinoma.

      Methods

      We present a case of small cell carcinoma with rhabdomyoblastic differentiation, diagnosed in a patient encountered in our practice.

      Results

      A 74-year old woman with a 60-pack-year smoking history and without prior medical history was hospitalized with mixed respiratory failure, felt to represent an acute exacerbation of chronic obstructive pulmonary disease. A computed tomography (CT) scan of the thorax revealed a solid spiculated right upper lobe nodule (1.1 cm) and a solid lobulated right middle lobe nodule (0.6 cm). Three months later, follow-up CT thorax revealed no change in these two nodules, but a new solid left lower lobe branching tubular density (2.2 cm), suspected to represent mucous plugging, was noted.

      Positron emission tomography (PET) CT scan was delayed by patient factors, but completed another three months later -- this revealed enlargement and intense FDG uptake in the left lower lobe density (SUV max, 9.7), and low-grade uptake in the stable right upper lobe nodule (SUV max, 1.5).

      She underwent transthoracic needle core biopsy of the left lower lobe nodule, revealing a cellular malignant neoplasm. The majority of malignant cells were small, round to oval, with high nuclear-to-cytoplamic ratio, fine chromatin, and indistinct nucleoli; a subset of malignant cells had rhabdomyoblastic features, including some with abundant densely eosinophilic cytoplasm and others with rhabdoid morphology (Figure 1). Immunohistochemical studies revealed reactivity of the small malignant cells to CKAE1/AE3 (focal), CK8/18 (focal), CD56, and synapthophysin antibodies, and of the rhabdomyoblasts to desmin, MYF, and myogenin (Figure 2) antibodies; Ki-67 proliferative index exceeded 90%. BRG1 immunohistochemical reactivity was preserved in the malignant cells.

      A fluorescence in situ hybridization study revealed no rearrangement of the FOXO1 gene. A clinical RNA-based next-generation sequencing assay was performed to test for the presence of rearrangements involving targeted regions of 138 fusion genes associated with sarcomas -- pathogenic rearrangements were not identified.

      The findings established the diagnosis of small cell carcinoma with rhabdomyoblastic differentiation.

      High-dose stereotactic body radiation therapy was provided to the left lower lobe nodule, with significant size reduction. However, bulky mediastinal lymphadenopathy was detected three months after treatment, and no further treatment was provided.

      Conclusion

      This report describes a case of small cell carcinoma associated with rhabdomyoblastic differentiation, an occurrence not previously reported in the literature.

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