John R. Tkach, M.D.
300 North Willson, Suite 203B
Bozeman, MT 59715
(406) 587-5442

Keratoacanthoma, K.A. for short (pronounced "care-at-oh-a-can-thoma")

Patient Information Sheet

Keratoacanthoma is a fleshy, pink to red, dome-shaped tumor that grows rapidly in 4-8 weeks and has a noticeable central plug or core of dead skin. The rapid growth and odd appearance often are scarey. Even without knowing what it is, most people know it is not right and should be taken care of. A true keratoacanthoma is not cancer in my opinion. If left alone, true K.A.'s may tend to shrink and resolve on their own after months. They may leave behind a small scar. Often there is no scar.

By the way, "tumor" refers to a swelling. It includes cancer and conditions that are not cancer. It does not automatically mean cancer.

What is it, and what should be done about it?

To answer these questions and update my knowledge, I did a literature search on K.A. on the MSU library's computer system on 2/27/2012. They are pretty tolerant of me up there. Until about 1957, dermatologists and pathologists called these tumors "self-healing squamous cell cancer."

In 1957, Dr. Kopf in New York City pointed out that this name does not make sense. The new term, keratoacanthoma, replaced it. After 1986, experience made it apparent that some tumors that clinically looked like K.A. were actually squamous cell cancer. Doctors began to view K.A.'s as the mild end of a spectrum with K.A. on one end and squamous cell cancer on the other end. Unfortunately, we do not have a pathology stain to tell cancer from non-cancer.

When examined under the microscope, K.A.'s look somewhat like squamous cell cancer. But, there are some differences. K.A.'s tend to be symmetric and have a central core of dead skin. The skin at the edges swoops down in fingers or a collar-like shape. Some areas of the tumor have skin cells with an odd ground glass appearance inside the cells. Squamous cell cancer looks more wild and disorganized, invades surrounding tissue, lacks the collarette and ground glass appearance, and has many skin cells in the cell division phase of growth (mitosis).

However, even with new, sophisticated immunohistochemical stains, it can be difficult to distinguish between K.A. and true squamous cell cancer. I have noticed over the past 15 years, that to be on the safe side, pathologists are tending to call more of these K.A.'s well differentiated (mild) squamous cell cancers.

Keratoacanthoma or K.A.

Keratoacanthoma on the temple.

Treatment options

  1. Freeze with liquid nitrogen. My experience since 1972 has been that if caught early while still small, 70% of K.A.'s will go away with liquid nitrogen freezing. I freeze it three times in a row in one visit (triple whammy). This should stop the rapid growth in 2 weeks, and the K.A. should be much better in 1 month. If not, I refer these for excision by a surgeon. Freezing works best with small K.A.'s.
  2. Excision. Surgery is always a right choice. It has two advantages. It gets rid of the tumor. It lets the pathologist examine the tumor and make the diagnosis. This is called doing a biopsy and is the gold standard. I often encourage patients to have excision for large K.A.'s rather than freezing them or waitng.
  3. No treatment. Wait and watch. This was old standard approach even up to 1986. I tend not to advise this, at least, especially for large K.A.'s. According to Barneston and Halliday (1997), nearly all the (K.A.'s) regress completely. The mechanism of spontaneous resolution is unknown but there is some evidence that it is mediated by CD4+ T-lymphocytes and apoptosis-inducing factor (Barneston and Halliday (1997), and Skyrlas (2011)).

In a study by Griffiths (2004) of 14 patients, spontaneous regression was complete. The average age of his patients was 65 (range 42-86). The average duration at first visit to the doctor was 9 weeks (range 4-28 weeks). The average time from appearance to spontaneous resolution was 27 weeks (range 12-64 weeks. It seems to me that this is a long time to put up with a tumor. Getting it removed after the first month or two would buy peace of mind.). Griffiths followed his patients an average of 3 years, 5 months (range 9 months-8 years).

In response to Griffiths' study, Leong reported that spontaneous resolution went faster when he removed the central plug of dead skin. I could not find anything in the literature to support this.

My contribution to the study of K.A. was a paper Keratoacanthoma of the glans penis, Tkach, John R., Cutis, 1979 Dec;24(6): 615-6. In 1974, an elderly man came to see me, when I was a resident, in my clinic at Denver General Hospital for a tumor on the end of his penis. I referred him to urology for simple excision of a K.A. The urologists were certain it was squamous cell cancer and scheduled him for amputation of the penis. There ensured a big battle between the urology and dermatology departments. We dermatologists convinced the urologists not to amputate. They did a simple excision. It healed with no scar or deformity and he did well.

This case was important for two reasons: 1. How many men in America are having their penises amputated annually for K.A.'s when it could have been avoided? 2. What does it tell us about the cause of K.A.? It is generally thought that K.A. arises from sun exposure or in hair follicles. The tip of the penis has no hair and is not exposed to the sun. In my opinion the cause of K.A. remains a mystery.

The information provided in these patient information sheets is offered for general informational and educational purposes only; it is not offered as and does not constitute medical advice. In no way are any of the materials presented meant to be a substitute for professional medical care or attention by a qualified practitioner, nor should they be construed as such.

Schedule your appointment today.