Reports say Artyom Sidorkin, 28, from the Urals region of Russia, is believed to have inhaled a seed which then sprouted inside him.
Doctors were convinced he had cancer after he came to them complaining of agonising chest pains and coughing up blood.
An X-ray showed what was believed to be a tumour, and he was rushed to the operating theatre.
Surgeon Vladimir Kamashev from Izhevsk in the Urals was quoted as saying "We were 100% sure."
"We did X-rays and found what looked exactly like a tumour. I had seen hundreds before, so we decided on surgery."
Before removing the major part of the man's lung, the surgeon investigated the tissue taken in a biopsy.
"I thought I was hallucinating," said Dr Kamashev.
"I asked my assistant to have a look: 'Come and see this - we've got a fir tree here'."
"He nodded in shock. I blinked three times as I was sure I was seeing things."
The 2in (5cm) spruce, which was said to be touching the man's capillaries and causing severe pain, was removed.
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http://news.sky.com/skynews/Home/World-News/Tree-Found-...
