PMC9893401_01
(a) A diagram of the ETV6-NTRK3 fusion. (b) A diagram of the CRTC3-NTRK3 fusion. (c) The tumor showed a predominantly microcystic architecture. (d) The specimen was composed of polygonal tumor cells with enlarged, round to oval nuclei and vacuolated, eosinophilic cytoplasm, and cystic spaces were remarkable for dense eosinophilic secretions.
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With these findings, the case was signed out as invasive ductal carcinoma (IDC) with secretory features (Figure 1). This evaluation confirmed both the ETV6-NTRK3 and CRTC3-NTRK3 fusions on orthogonal tissue-based sequencing (Figure 1).
(a) A timeline of the patient's clinical story, including treatments below the timeline and biopsies and clinical response above the timeline. (b) The left CT chest images demonstrate numerous pulmonary and pleural metastases. The images on the right show marked improvement of these lesions after 2 months of larotrectinib. The decrease in the MAF of the two NTRK3 fusions is demonstrated in between the CT images.. ADC, antibody-drug conjugate; CT, computed tomography; ddACT, dose dense doxorubicin + cyclophosphamide followed by paclitaxel; PARP inh, poly adenosine diphosphate-ribose polymerase inhibitor.
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Repeat Guardant testing on a subsequent blood sample showed a reduction in the ETV6-NTRK3 fusion MAF from 10.90% to 0.40%, and the CRTC3-NTRK3 fusion MAF from 3.20% to 0.07% (Figure 2).