Can stage 1a endometrial cancer (removed) spread to mediastinal, bilateral hilar and virchow's node w/o infiltrating another organ?

Yes but: It could possibly spread to local lymph node but the chances are very low. The lymph nodes that are in thoracic cavity are even less likely to contain metastatic tumor from a stage 1a endometrial cancer, especially if it's a garden variety low grade lesion. In fact, long term survival is very good, like 95%. The other 5% may represent very high grade tumors.