In a 71-year-old patient with a 0.5 cm lesion behind the right ear present for one year without itching, bleeding, or prior skin cancer, what is the most likely diagnosis?

Differential Diagnosis: Stable Posterior Auricular Lesion in a 71-Year-Old

This lesion most likely represents a benign entity such as seborrheic keratosis, epidermoid cyst, or pilomatricoma, but given the patient's age and the auricular location, excisional biopsy is mandatory to definitively exclude basal cell carcinoma, squamous cell carcinoma, or melanoma.

Clinical Assessment Framework

The absence of itching, bleeding, or change over one year argues against malignancy, but these features are not sufficiently reliable to exclude skin cancer in a 71-year-old patient with an auricular lesion 1.

Key Clinical Features to Evaluate

Examine the lesion for:

• ABCDE criteria for melanoma 1:

  • Asymmetry
  • Border irregularity
  • Color heterogeneity (multiple shades of brown/black)
  • Diameter >7mm (this lesion is 5mm, but size alone doesn't exclude melanoma)
  • Evolution (recent change) - notably absent in this case

• Seven-point checklist 2:

  • Major criteria: change in size, color, or shape
  • Minor criteria: diameter ≥7mm, sensory change, inflammation, crusting/oozing/bleeding
  • This lesion appears to lack these features

• Basal cell carcinoma features 3:

  • Pearly or translucent appearance
  • Telangiectasias
  • Central ulceration
  • The ear is a high-risk location for BCC with increased metastatic potential

Most Likely Diagnoses

Benign Entities (More Probable Given Clinical Stability)

Seborrheic keratosis is common in this age group and can occur behind the ear 1, 4. These lesions typically appear as "stuck-on" waxy growths with a warty surface. However, posterior auricular location is uncommon 4, and one case report documented misdiagnosis where SK was initially suspected but squamous carcinoma was ultimately confirmed 5.

Epidermoid/sebaceous cyst can present as a firm, mobile nodule behind the ear 6. These are typically asymptomatic unless infected.

Pilomatricoma is a benign hair follicle tumor that, while rare in the auricle, has been documented in this location 7, 8, 9. It presents as a firm, slow-growing nodule.

Malignant Entities (Must Be Excluded)

Basal cell carcinoma of the ear carries higher recurrence and metastatic risk compared to other sites 3. The ear is considered a high-risk "H-zone" location.

Squamous cell carcinoma can present as a non-healing lesion and has higher metastatic potential when arising on the ear 10.

Melanoma of the external ear accounts for 1-4% of cutaneous melanomas 11. The lack of evolution over one year makes this less likely but doesn't exclude it entirely 1.

Critical Management Recommendation

Perform excisional biopsy with 2mm margins under local anesthesia 1. This is the standard approach for any suspicious cutaneous lesion in this age group and location.

Rationale for Excisional Biopsy

The guidelines are unequivocal 1:

• Complete excision is preferred over incisional biopsy to avoid sampling error
• Allows full histopathological assessment of the entire lesion
• If benign, no further treatment needed
• If malignant, provides accurate staging (Breslow thickness for melanoma, depth of invasion for other cancers)
• Partial biopsies risk missing deeper infiltrative components

Common Pitfall to Avoid

Do not assume benignity based on clinical stability alone 5. One case report documented a posterior auricular lesion initially diagnosed as seborrheic keratosis through multiple biopsies over 10 years, but clinical appearance suggested malignancy. Final diagnosis after complete excision was squamous carcinoma 5. This underscores that when clinical observation conflicts with initial pathology, pursue complete excision.

Surgical Approach

• Use scalpel excision (not laser or electrocautery) to preserve tissue architecture 1
• Orient incision to facilitate potential re-excision if margins are positive
• Send entire specimen for histopathology with patient age, sex, and lesion site documented 1
• For posterior auricular location, reconstruction may require local flaps if defect is large 4

The definitive diagnosis cannot be established without histopathological examination, regardless of how benign the clinical presentation appears 1, 12.