 In addition to Mackenzie's opinion, Bismarck strongly opposed any major operation on Frederick's throat, and pressed the Kaiser to veto it.On 9 June, Mackenzie again biopsied the growth and sent the samples to Virchow, who reported the following day that he was again unable to detect any signs of cancer.On 13 June, the Crown Prince left Potsdam for London to attend his mother-in-law's Golden Jubilee and to consult Mackenzie.