Cutaneous horns: clues to invasive squamous cell carcinoma being present in the horn base

Background: Cutaneous horns usually develop on a keratinocytic base with the histopathology on a spectrum ranging from benign keratosis through to invasive squamous cell carcinoma (SCC). Some features of horns are easily identified using dermatoscopy. Objective: To investigate if specific clinical or dermatoscopy features of horns correlate with the histopathology in the base of the horn. Methods: Consecutive horn cases (n=163) were assessed prospectively in vivo for horn height, terrace morphology and base erythema using a Heine Delta 20 dermatoscope. Cases with potentially confounding influences were excluded. A history of horn pain or pain on palpation was also recorded. Results: Benign keratosis (n = 49), actinic keratosis (n = 21), SCC in situ (n = 37) and invasive SCC (n = 56) were recorded. An invasive SCC presenting as a horn as most likely to have a height less than the base diameter, 66% (37/56). Compared to the other study entities, invasive SCC tends to have less terrace morphology (P<0.05), a higher incidence of base erythema (P<0.05) and more pain (P<0.01). Limitations: Data categories did not include anatomic site or horn growth rates. Excision selection bias favored the incidence of invasive SCC. Conclusions: Horns presenting on an invasive SCC base are more likely to have a height less than the diameter of the base, not to have terrace morphology, to have an erythematous base and to be painful.


Introduction
Cutaneous horns are usually found on chronic sun damaged skin. Horns are conical shaped, circumscribed and composed of dead keratin usually derived from base keratinocytes. Anatomic sites for horn predilection include the exposed areas on the head, the dorsa of the hands and forearms. A horn base may display benign or malignant histopathology. Horns with a benign histopathological base have a reported incidence ranging from 41% [1] to 60% [2,3] and up to 77% on the eyelid [4]. Horn formation can occur in keratoacanthoma [5]. Squamous cell carcinoma has been reported in 94% of horns with a malignant base [1]. Factors previously reported to be associated with premalignant and malignant Cutaneous horns: clues to invasive squamous cell carcinoma being present in the horn base

Exclusion criteria
Any horn with a known history of prior intervention was excluded, this included previous ablative therapies, topical medication either clinician or patient initiated, previous surgery and horns in a field of previous photodynamic therapy or radiotherapy. Horns in contact with tattoos or scars and collision situations where non-horn entities were identified together with a horn either during clinical examination, dermatoscopy or on histopathological section were also excluded. Horns on a non-keratinocytic base were not encountered during the study window.

Definitions of the horn features assessed
(1) Horn heights were compared to the diameter of the base of the horn. The height was recorded as either less than the base diameter or greater or equal to the base diameter, or up to a height twice the base diameter or greater than twice the base diameter. Such horn height assessment is very quick to perform and easy to do in practice.
(2) Terrace morphology is a feature characterized by structural horizontal contours on the side of the horn, as demonstrated by Figure 1A and B. An example of a horn without terrace morphology is shown in Figure 2A and Figure 2B. horns are male sex, increased age, anatomic site and lesion geometry [2]. Wide base or low height-to-base ratio horns are more likely to display a malignant base [2]. Multiple horns may occur on some patients. Actinic keratoses have been reported as the most common horn base entity (37.4%) in a study of 230 horns [6]. Horns associated with likely invasive SCC at the base should be identified and receive pri-

Prospective in vivo data collection occurred from July 2009
to April 2011 in a private practice in Sydney, Australia. All 163 cases were submitted for routine histopathology then allocated into one of the following four categories: benign keratosis; actinic keratosis; SCC in situ or invasive SCC.
Horns with a seborrheic keratotic base were included in the benign keratosis category. Data was recorded in vivo using a Delta Heine 20 dermatoscope (Heine, Optotechnic GmbH, Herrsching, Germany). Photographs were recorded using a Canon EOS 550D camera (Canon, Tokyo, Japan) coupled to a DermLite FOTO dermatoscope (3Gen). To avoid diagnostic error due to inadequate tissue that is too superficial, all excisions were taken down to subcutaneous fat. In a previous horn study [6], some cases under investigation were unable to be confidently diagnosed due to insufficient excision depth.

Data validation
To assess interobserver agreement between two observers (JP

Results
Invasive SCC 34.4% (56/163) was the most common histopathology at the horn base in this study with Study data in Figure 6 indicates that pain was most fre-

Horn pain
A history of horn pain or pain on palpation was recorded in 48%, CI: 35.7-61.0%, (27/56) of invasive SCC; see Figure   6. Invasive SCC had the highest recorded incidence of pain compared to the other diagnostic categories, P = 0.007.  serve more as diagnostic indicators rather than for precise diagnostic confirmation.
Findings from this study indicate that when presenting as a horn, invasive SCC most likely has a height less than the diameter of the base; does not have terrace formation; displays base erythema; and may possibly be painful.
Whether present or absent, there was no feature in this study that alone confidently confirms or excludes the prehistopathological diagnosis of invasive SCC at a horn base.