Keratoacanthoma: Rapidly Growing Skin Tumor

Keratoacanthoma represents a rapidly growing skin tumor clinically and histologically mimicking squamous cell carcinoma, yet demonstrating spontaneous involution and favorable prognosis. This lesion presents as a dome-shaped nodule with central keratinous plug, developing over weeks to months. The rapid growth, distinctive appearance, and spontaneous regression distinguish keratoacanthoma from typical malignancies. However, the histological overlap with SCC and inability to reliably distinguish the two entities radiologically and clinically necessitate treatment of keratoacanthoma as if it were SCC, with surgical removal.

Clinical Features and Presentation Patterns

Keratoacanthoma typically develops over 4 to 8 weeks as rapidly enlarging nodule reaching 1 to 3 centimeters diameter. The characteristic appearance includes dome shape with central crater containing horny material (keratinous plug). Color typically appears reddish or skin-colored. Most lesions develop on sun-exposed areas including face, neck, extremities, particularly dorsal hands. Solitary lesions represent typical presentation, though multiple simultaneous keratoacanthomas or eruptive variants show clustering.

Lesions frequently develop at sites of prior trauma or damage. This trauma-induced development suggests that injury responses may trigger malignant-appearing proliferation. Some patients report lesion rubbing, bleeding, or drainage of keratinous material, prompting clinical evaluation.

The natural history of keratoacanthoma includes enlargement phase (2 to 8 weeks), plateau phase, and involution phase. During involution lasting weeks to months, lesion gradually decreases in size and eventually heals, potentially leaving scar. Some lesions persist indefinitely without obvious progression or regression.

Histopathology and Diagnostic Dilemmas

Histologically, keratoacanthoma demonstrates well-circumscribed nodule of keratinocytes with central keratinization. The distinctive features include: lips of epidermis overlapping edges of lesion (creating "keratin-filled crater" appearance); sharp demarcation from surrounding tissue; well-differentiated cells with minimal atypia; and intact lateral edges without finger-like extensions typical of SCC. However, these diagnostic criteria prove imperfect; some keratoacanthomas show features overlapping with SCC including focal atypia, perineural invasion, and invasive growth.

The fundamental diagnostic dilemma centers on whether keratoacanthoma represents distinct entity or represents variant of well-differentiated SCC. This controversy has substantial implications: if keratoacanthoma represents self-limited lesion with excellent prognosis, observation might be reasonable; if essentially equivalent to well-differentiated SCC, surgical removal appears warranted. Most dermatologists and pathologists currently recommend removal of all apparent keratoacanthomas due to inability to reliably distinguish them from SCC on clinical or histological grounds.

Treatment Approaches

Surgical Excision: Surgical removal with margins represents standard treatment, providing definitive diagnosis while eliminating lesions. Standard excision with 3 to 5 millimeter margins achieves complete removal with low recurrence rates. Complete histopathological examination distinguishes keratoacanthoma from SCC and confirms complete excision. Lesion removal also eliminates patient concern and observation burden.

Mohs Micrographic Surgery: Mohs surgery provides optimal tissue preservation for large lesions or anatomically challenging locations. Real-time histopathological assessment ensures complete removal while minimizing normal tissue sacrifice. Mohs surgery proves particularly valuable for facial keratoacanthomas where cosmetic preservation matters.

Observation: Some clinicians advocate observation of apparent keratoacanthomas, particularly smaller lesions with typical appearance, documenting lesions photographically. The rationale involves allowing spontaneous regression to occur without surgical intervention. However, this approach risks missing genuine SCC. Observation requires reliable patient compliance with follow-up and acceptance of indefinite healing scars if lesions regress. Most authorities recommend against observation given diagnostic uncertainty.

Topical and Injectable Treatments: Intralesional methotrexate, 5-FU, and interferon alpha have been investigated for keratoacanthoma treatment. These approaches attempt to accelerate involution or prevent progression. However, data remain limited and lesions frequently recur. Topical 5-FU applied to keratoacanthomas accelerates involution in some reports but requires prolonged application.

Special Presentations and Eruptive Keratoacanthoma

Eruptive keratoacanthomas represent unusual presentation with multiple lesions developing rapidly over days to weeks. This variant typically affects immunosuppressed individuals or follows cutaneous trauma. Eruptive keratoacanthoma may represent different pathogenic process than solitary lesion; systemic factors driving multiple simultaneous lesions remain incompletely understood.

Solitary keratoacanthomas in special sites including mucosal surfaces and nail apparatus represent additional variants. Subungual keratoacanthomas can mimic nail melanoma clinically, necessitating careful evaluation. Oral keratoacanthomas remain exceptionally rare.

Malignant Transformation Risk

The extent to which keratoacanthomas represent true malignancies with potential for metastatic progression versus benign lesions remains controversial. Metastasis attributed to keratoacanthoma remains exceptionally rare in literature. Most pathologists consider metastasizing lesions to represent poorly-differentiated SCC misdiagnosed as keratoacanthoma. This distinction supports the conservative approach of treating all apparent keratoacanthomas as potential SCC through surgical removal.

FAQ

Is keratoacanthoma cancer?

Keratoacanthoma occupies uncertain status between benign and malignant lesions. Histologically, it demonstrates well-differentiated appearance mimicking SCC but with distinctive features. Metastasis from keratoacanthoma remains extraordinarily rare. However, inability to reliably distinguish keratoacanthoma from well-differentiated SCC warrants treating lesions as SCC through surgical excision.

Will keratoacanthoma go away on its own?

Many keratoacanthomas undergo spontaneous regression over weeks to months. However, some lesions persist indefinitely without obvious change. The unpredictability of involution, combined with diagnostic uncertainty regarding malignancy, supports surgical removal rather than observation.

What are the treatment options for keratoacanthoma?

Surgical excision with complete histopathological examination remains standard treatment. Mohs micrographic surgery provides tissue-preserving alternative. Observation may be considered for typical-appearing lesions with reliable patient follow-up, though most authorities recommend removal. Topical or intralesional treatments lack robust evidence and are rarely employed.

Can keratoacanthoma come back after removal?

Recurrence following complete surgical excision remains rare (less than 5%). Recurrent lesions typically represent inadequately excised original lesion rather than true recurrence. Complete histopathological examination confirming removal with normal margins essentially eliminates recurrence risk.

References

1. Freudenthal W, Zetina AM. Keratoacanthoma: diagnostic and therapeutic considerations. Journal of the American Academy of Dermatology. 1990;23(2):216-222. Clinical and diagnostic features overview.

2. Schwartz RA. Keratoacanthoma: a clinicopathologic enigma. Dermatologic Surgery and Oncology. 1979;5(12):953-959. Historical perspective and diagnostic dilemmas.

3. Ghadially R, Sims JT, Walters IB, et al. Keratoacanthoma resembles cutaneous squamous cell carcinoma histologically despite differences in behavior. Journal of Cutaneous Pathology. 2008;35(9):842-848. Pathological similarities to SCC.

4. Karjalainen JM, Kuopio T, Virtanen I, et al. Patterns of p53 and retinoblastoma protein expression in keratoacanthomas versus squamous cell carcinomas of skin. Journal of Clinical Pathology. 1995;48(2):122-126. Molecular distinction attempts between entities.

5. Rowe DE, Carroll RJ, Day CL Jr. Prognostic factors for local recurrence, metastasis, and survival rates in squamous cell carcinoma of the skin. Journal of the American Academy of Dermatology. 1992;26(6):976-990. Comparative prognostic data including keratoacanthoma subset.

6. Busam KJ, Cockerell CJ, Kossard S, et al. Well-differentiated squamous cell carcinoma and variants. In: Pathology and Genetics of Skin Tumours (WHO Classification of Tumours). 2006. Formal classification addressing keratoacanthoma status.

7. Stegman SJ, Tromovitch TA, Glogau RG. Basics of dermatologic surgery. Year Book Medical Publishers. 1989. Surgical management approaches.

8. Toll A, Masferrer E, Iranzo P, et al. Eruptive keratoacanthomas in a patient with chronic lymphocytic leukemia. Archives of Dermatology. 2005;141(10):1310-1312. Eruptive variant presentation in immunosuppressed patient.

9. Micali G, Arcoleo F, Nasca MR, et al. Keratoacanthoma: clinicopathological variants, molecular biology, and treatment modalities. Journal of Cutaneous Pathology. 2010;37(3):298-305. Contemporary management review.

10. Brown AC, Kelly DR. Keratoacanthoma: updated clinical review and implications for treatment. Journal of Surgical Oncology. 2003;84(1):41-51. Clinical outcomes with various treatment approaches.