 A room on the top floor of the Crown Prince's palace was then equipped as an operating theatre, but Bergmann elected to put the operation on hold until Mackenzie could provide his assessment.Mackenzie arrived in Berlin on 20 May, but after examining Frederick recommended a biopsy of the growth to determine whether or not it was malignant.He conducted the biopsy the following morning, after which he sent tissue samples to the distinguished pathologist Rudolf Virchow for microscopic examination.