The Importance of Pathogenesis: A Molecular Investigation on A Solitary Choriocarcinoma Lung Lesion with No Primary Lesion

Abstract Introduction/Objective We present an exceedingly rare case of metastatic choriocarcinoma to the lung with no primary lesion. Notably, this is the only case where STR molecular studies have been conducted. Methods/Case Report A 43-year-old G1P1001 female with no past medical history presents with severe shortness of breath, left-sided back, and chest pain for severe shortness of breath, left sided back and chest pain. Patients pregnancy test was positive with a B-hCG of 17944 u/L. Transvaginal ultrasound was negative for IUP. CTAP showed no masses in the uterine cavity or ovaries. D-dimer was elevated at 623 ng/ml. However, CTA chest was negative for pulmonary emboli but revealed a RLL mass measuring 2.6 x 2.5 cm x 2.9 cm with lobulated areas suspicious for vascular structures and connection to the right pulmonary vein. Patient was treated with a complete right lower lobectomy. An endometrial biopsy was performed and was negative for malignancy with no significant findings. Grossly, the mass was well-circumscribe, hemorrhagic, and necrotic, measuring 3.5 cm. Microscopically, the malignant cells had highly pleomorphic and hyperchromatic nuclei. There were also multiple multinucleated cells and mitotic figures present. Some of the cells had nested architecture leading to us to suspect a pleomorphic lung adenocarcinoma with choriocarcinomatous differentiation. We performed IHC staining that demonstrated strong positivity of AE1/AE3, CK7, hCG and a high Ki-67 index. The neoplastic cells also had focal p63 and p40 positivity. Furthermore, TTF1 and SALL4 were both negative. This staining pattern as well as patient’s clinical history of no gynecological lesion, lead us to favor lung adenocarcinoma with choriocarcinomatous differentiation. However, due to the abundance of syncytiotrophoblastic and trophoblastic cells, metastatic choriocarcinoma could not be ruled out. Therefore, the case was sent out for external consultation and Short Tandem Repeat (STR) molecular testing. Surprisingly, the STR testing results showed some STR of paternal origin indicating a metastatic gestational choriocarcinoma. The patient’s surgery was highly successful and lead to a down trending of b-hCG from 17944 to 1768 after removal. Results (if a Case Study enter NA) NA Conclusion Performing STR testing was pivotal in this case as it revealed the presence of DNA of paternal origin, providing crucial evidence that the tumor was of gestational origin, guiding the diagnosis towards metastatic gestational choriocarcinoma.