The Workers’ Compensation Court of Appeals, with one judge dissenting, awarded Walter Schopf compensation for a permanent partial disability of his right hand and for temporary total disability from July 17, 1979, to August 19, 1979, pursuant to a finding that the lipoma which had caused his disabilities was work-related. Relators, Red Owl Stores, Inc., and its compensation insurer sought review, claiming that employee did not establish a causal relationship between the tumor and his employment by a preponderance of the evidence. We disagree and affirm the award.
Employee testified that over a 15-year period he opened an average of 200 cartons of groceries each day with a cutter, a tool held across the palm of his right hand, and stamped price marks on their contents, usually 24 cans or boxes, with a stamper. Employee also held the stamper in his right hand, its ball-shaped top cupped in the palm, and operated it by placing the marking end of the tool on the item to be priced and putting pressure on the ball with his fingers. In the early 1970’s he developed a swollen area the size of a half dollar in the palm of his hand near his thumb. It did not then cause him pain or discomfort, but he showed his hand to his family doctor, Dr. Myles Efteland, in March 1975 and the doc*802tor suggested he wear a glove to protect his hand. The tumor gradually grew larger and more firm, and by 1977 employee’s fingers felt numb. Ultimately he could hardly close his hand or grasp with it and tried to do his work with his left hand. He found this ineffective and consulted Dr. Efteland in May 1979.
Dr. Efteland referred employee to Dr. Peter Vogt, a reconstructive surgeon, who removed the tumor on July 17, 1979. The surgeon found that' the tumor was well encapsulated and so large that it had stretched the medial nerve in employee’s hand. Employee returned to work a month later but had some weakness in his hand. The medical witnesses agreed that he had sustained a 20% permanent partial disability but disagreed on whether there was a causal relationship between employee’s work and the development of the tumor.
Dr. Efteland expressed the opinion that the development of the tumor could be causally related to employee’s work, adding:
It seems quite reasonable to me that with that type of occupation, with repetitive pressure upon that involved area over a period of at least five years, that there could be a causal relationship.
He had reached this opinion after research in a publication by the Armed Forces Institute of Pathology and an article published in the Journal of Bone and Joint Surgery in June 1965 by Dr. Robert Booker, Lipoblastic Tumors of the Hands and Feet. Dr. Efte-land said also that in his opinion employee’s work had stimulated the growth of the tumor. On cross-examination he conceded that the etiology of tumors is not known. The following exchange also occurred:
Q. And, as I understand it, it is not your opinion that the lipoma that you observed or the tumor was caused by this man’s employment?
A. No, that’s not correct. It’s my opinion it could very well have been caused by his employment.
Q. Can you say to a reasonable degree of medical certainty that it was caused by his employment?
A. I cannot prove it in a court of law, no.
Dr. Vogt, a board-certified plastic surgeon, expressed the opinion that the tumor was not work-related and “came about by itself just as most lipomas do.” He added that an encapsulated lipoma is not related to trauma and that repeated trauma to an existing tumor might cause it to become scarred, but not necessarily enlarged. He had seen no evidence of bleeding or scarring in the tumor.
Dr. Mark Johnson, a board-certified specialist in internal medicine who examined employee for relators, expressed the opinion that employee’s work had not caused the tumor or contributed substantially to its development. He also had reviewed the article by Dr. Booker and considered it a catalog of characteristics of tumors that the author had observed but not an attempt to ascribe etiologic factors in the cases described. Dr. Johnson agreed that the etiology of lipomas is not clear and said they typically have a slowly progressive course. He felt that if employee’s tumor had been subjected to substantial trauma it would have been inflamed or scarred. He conceded, however, that employee’s hand had been exposed to substantially more trauma than that to which most people are exposed. He agreed that employee’s use of the tools could have caused some trauma to the tissue of his hand even if it did not result in scarring and also said that he would have advised employee in 1975 not to use the stamper in order to avoid injuring the tumor.
The compensation judge found that employee had sustained a personal injury to his hand as a result of his work activities, accepting Dr. Efteland’s opinion in preference to that of the other medical witnesses. On appeal, the majority of the Court of Appeals affirmed, agreeing that Dr. Efte-land’s opinion was more credible than that of the other medical witnesses. Although aware that we have repeatedly recognized that resolution of conflicts in medical opinions is the function of the Court of Appeals, relators urge here that employee did not prove causal relationship between bis work *803and the disabling tumor by a preponderance of the evidence because Dr. Efteland’s opinions that the tumor was caused and that its growth was accelerated by employee’s work were speculative and lack reasonable medical certainty.
We do not agree. The doctor’s commendably candid statement upon cross-examination that he could not “prove it in a court of law” was obviously a way of stating that he could not speak with absolute certainty, but he was not required to do so. His testimony, viewed as a whole, clearly shows that his basic opinion was that the repeated trauma employee’s hand received in the course of his work had probably caused and had stimulated the growth of the tumor.1 It is well established that a medical opinion does not have to express absolute certainty, its truth need not be capable of demonstration, and it is sufficient if it is probably true. Sullivan v. Hagstrom Construction Co., 244 Minn. 271, 278, 69 N.W.2d 805, 809 (1955). Nor does the fact that the etiology of tumors is not known render the doctor’s opinion speculative. Boldt v. Jostens, Inc., 261 N.W.2d 92, 93 (Minn.1977). Since the Court of Appeals properly considered Dr. Efteland’s testimony as well as that of the other medical witnesses, we will not interfere with its determination that his testimony on the issue of causation was the most credible.
We conclude that employee has sustained his burden of proving by a preponderance of the evidence the requisite causal relationship between his work and the lipo-ma.
Employee is awarded attorneys’ fees of $400.
Affirmed.
. Employee had used the stamper over a million times.