Professor Peter Mallmann told The Local he required the help of two assistants to lift the 60-centimetre wide tumour out of the woman, who is expected to make a full recovery.
The tumour weighed 14.3 kilos - around four times the weight of a newborn baby which are generally around 3.5 kilos.
“She said she had first noticed something just six months ago,” he said. “But I find it difficult to believe she had really not realised something was wrong before that. People do tend to push things like that into the back of their minds.”
She weighed around 60 kilos, he said, while the tumour was just over 14 kilos. Mallmann and a team at the Cologne University Hospital removed it about a week ago.
One of her ovaries had been affected by the benign cancer, which had effectively turned it into a huge balloon of slime, he said.
He said the 54-year-old woman, who has asked not to be identified, was in danger of suffering an intestinal obstruction because the tumour had grown so large it was squeezing her internal organs together. Such an obstruction can be fatal.
A man would have suffered much more discomfort from such a growth, said Mallmann, as they are much less flexible. “Women's bodies are designed to accommodate babies which are essentially large internal growths,” he said.
“This was the biggest tumour I have dealt with, but was not the biggest ever in Germany – one weighing 18 kilos was removed from a woman in Berlin in 2008, so this one does not get into the Guinness Book of Records, but it would certainly get into the top five.”
The woman has already gone home and is expected to make a full recovery. “She is, in every sense of the word, relieved,” said Mallmann.