TNC's Weed Team has been looking into the link between knapweed and cancer suggested in an e-mail message by Jerry Niefoff of Idaho Panhandle National Forest which was widely distributed in early September, 1997. None of our sources here at Davis or elsewhere had heard of such a link before and some questioned whether we might be dealing with a hoax.

Nonetheless, the possibility that knapweeds may contain a carcinogen has serious implications for us. Knapweeds (Centaurea spp.) are problem weeds on many of our preserves across the nation and our stewards and volunteers pull, mow, burn and/or herbicide them.

What we know so far...

To paraphrase Niefoff's message (full text copied below): he pulled knapweed barehanded getting sap into breaks in his skin and afterward noticed pain in joints of the affected fingers. Months later he noticed a lump in his finger which turned out to an aggressive tumor that spread and in the end required amputation of the little finger and adjacent ring finger on his right hand. A doctor at the cancer center at the U. of Washington where he had surgery told him a compound in knapweed is cancer causing, that it was isolated in Russian knapweed and probably occurs in spotted and diffuse knapweed also.

Barry Rice (TNC Weed Team) spoke with Niefoff and confirmed that Jerry Niefoff works in the Forest Supervisor's Office and had his fingers amputated. Niefoff is convinced there is a connection with the tumours that developed in his hand and a day spent pulling knapweed.

Peter Dunwiddie (TNC WAFO) had his brother (a pharmacology prof) do some checking from the medical side. His brother replied that despite covering the entire medical literature back to 1966 he couldn't come up with anything that would corroborate any reports of carcinogenicity. He found references to a compound (repin) that is neurotoxic, and does bad things to the brains of horses that eat knapweed, but found nothing about carcinogens. A couple of papers he found suggested knapweeds contain compounds that are antibacterial and have ANTI-tumor properties, but nothing that would be consistent with Niefoff's report. Peter's brother said that occasionally when something like this happens, a physician will write a "case report" (i.e., "I had a patient who..."), but I couldn't even find anything like that. He believes the only references he would have missed is if there was something pre-1966 that has been completely ignored since, or if there is a compound in knapweed that is a well-known carcinogen, but for some reason none of the studies of this compound even mention knapweed.

Peter's brother also reported that none of the other compounds that are known to be in knapweed, like repin, cnicin, acetoxycnicin, melitensin, lappaol, etc., have been reported to have carcinogenic effects. He noted, however, that some plants make a whole slew of plant defense compounds, not all of which have been identified or characterized, and some of which could be nasty, and it may be that no one has discovered this yet.

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About 5 years ago, I had spent most of a mid July day pulling knapweed with my bare hands. At the end of the day, I had broken my skin on the little finger and the adjacent ring finger of my right hand. I also suspect that in pulling the knapweed, that I broke knapweed stems and got sap directly into my tissues, through the broken skin. I noticed that these injured sites in the joints of these two fingers were slow in healing and I always seemed to have pain in them. About 6 months later, I started to develop a lump in my little finger, so I decided to see my family doctor. He aspirated the lump and figured it was a cyst. He said it was in a bad location, lots of nerves and tendons and if it continued to bother me, I was suppose to see a hand surgeon and have it removed. About 6 months after my initial doctors visit, the finger got worse, so I went to the hand surgeon, he operated and found the lump to be what they call a very aggressive benign tumor. A month or two after the first surgery it came back only worse, so they operated again. After the second surgery, the tumor really started to spread towards the hand, so they removed the little finger. Shortly after the removal of the little finger, I started to get tumors in my ring finger. This time I went to the cancer center at the University of Washington. After several surgery's on that finger with the same results, they ended up removing that finger also.

The tumors all occurred in the tendon sheath, and they could never get it all until they removed the entire finger..

They cannot treat the tumors I had with chemo or radiation, only physical removal.

The doctor at the U of W said that there is a compound in knapweed that is cancer causing, this compound was isolated in Russian knapweed and probably occurs in spotted and diffuse knapweed also.

It has been two and a half years since my last surgery and no problems have occurred in my other fingers at this point.

If someone else can avoid what happened to me, I would be very pleased.
Jerry Niefoff
Soil Scientist
Idaho Panhandle National Forest