Keratoacanthoma (KA) and squamous cell carcinoma (SCC) are two common types of skin lesions that arise from keratinocytes, the primary cells of the skin’s outer layer. These growths can appear remarkably similar to the unaided eye, often causing confusion. Understanding their distinct characteristics, growth patterns, and behaviors is important for proper identification and management.
Defining Keratoacanthoma
Keratoacanthoma is a low-grade skin tumor known for its unique and predictable life cycle. It begins with rapid growth, often reaching 1 to 2 centimeters within six to eight weeks. Following this rapid expansion, the lesion enters a stable phase, maintaining its appearance for several weeks to months.
Keratoacanthomas then spontaneously involute, shrinking and healing on their own, often leaving a scar. This lesion presents as a flesh-colored or reddish dome-shaped nodule with a central crater filled with a keratin plug, often described as having a “volcano-like” appearance. While keratoacanthomas can self-resolve, they are often treated due to their resemblance to more serious skin cancers and for improved cosmetic outcomes.
Understanding Squamous Cell Carcinoma
Squamous cell carcinoma is the second most common type of skin cancer. Unlike the rapid growth and potential self-resolution seen in keratoacanthoma, SCC typically exhibits a slower, persistent growth pattern, evolving over months. This malignancy arises from the abnormal, accelerated growth of squamous cells, which are flat cells in the skin’s outer layer.
The appearance of SCC can vary, presenting as a scaly red patch, a firm nodule, or an open sore that may bleed, crust, and fail to heal. A distinguishing feature of SCC is its capacity to invade deeper tissues and potentially metastasize (spread) to regional lymph nodes or other parts of the body if left untreated. This potential for spread underscores its classification as a true malignancy.
Key Distinctions in Clinical Presentation and Growth
The observable differences between keratoacanthoma and squamous cell carcinoma center on their growth dynamics and morphology. Keratoacanthomas are characterized by exceptionally rapid growth, often developing to 1 to 2 centimeters within six to eight weeks. In contrast, squamous cell carcinomas exhibit a slower, steady expansion over several months. This difference in growth rate is an important initial indicator.
Regarding their physical appearance and shape, keratoacanthomas present as symmetrical, dome-shaped nodules with a central crater filled with a keratin plug, resembling a small volcano. Squamous cell carcinomas, however, tend to be more irregular in shape. They can manifest as flat, scaly red patches, firm nodules, or ulcerated sores that may crust or bleed. The central keratin plug, a hallmark of keratoacanthoma, is typically absent in SCC.
A fundamental distinction lies in their evolution: keratoacanthomas have the inherent potential to spontaneously shrink and resolve over several months, leaving a scar. Squamous cell carcinomas, conversely, do not resolve on their own and will continue to grow and expand into surrounding tissues if left untreated. Both lesions appear on sun-exposed areas of the body, such as the face, neck, hands, and arms, reflecting a shared association with ultraviolet radiation exposure.
Diagnostic Challenges and Procedures
Given the visual and microscopic similarities between keratoacanthoma and squamous cell carcinoma, a definitive diagnosis almost always requires a skin biopsy. This procedure is the standard and necessary step to distinguish between these two entities. Even for experienced pathologists, the distinction can be challenging because the individual cells of a keratoacanthoma and a well-differentiated SCC can appear nearly identical under a microscope.
The diagnosis relies on examining the overall “architecture” of the entire lesion, specifically how the cells are organized and if there is evidence of invasion into the surrounding tissue. For this reason, a deep excisional biopsy or a punch biopsy is often preferred over a superficial shave biopsy. A superficial biopsy might not provide enough tissue depth to accurately assess the lesion’s full structure and its interface with underlying subcutaneous tissue, which is preserved in keratoacanthoma but invaded by SCC. The ongoing discussion about whether keratoacanthoma is a distinct, self-resolving entity or merely a subtype of squamous cell carcinoma further highlights these diagnostic complexities.
Comparing Treatment Approaches and Prognosis
Surgical excision stands as the most common treatment approach for both keratoacanthoma and squamous cell carcinoma. For SCC, surgical removal is performed to eradicate the cancerous cells, prevent local tissue destruction, and halt any potential spread to other parts of the body. This intervention is crucial for a malignancy with metastatic potential.
For keratoacanthoma, surgical excision is often recommended even with its potential for spontaneous regression. This is largely because, until the entire lesion is examined by a pathologist, a definitive distinction from SCC can remain uncertain. Additionally, surgical removal often results in a better cosmetic outcome compared to allowing the lesion to spontaneously heal, which can leave a significant scar. The prognosis for a properly removed keratoacanthoma is generally excellent, with a low likelihood of recurrence or spread. In contrast, for SCC, the prognosis is also very good when caught and treated early. However, ongoing follow-up appointments are important to monitor for any signs of recurrence or the development of new lesions, reflecting SCC’s malignant nature and potential for spread, which is a key difference in the long-term outlook for patients.