What is infiltrative basal cell carcinoma?

What is Infiltrative Basal Cell Carcinoma?

Infiltrative basal cell carcinoma is a high-risk histologic subtype of BCC characterized by irregular finger-like tumor outgrowths that extend deeply and widely into surrounding tissue in a three-dimensional pattern, making clinical margins deceptively small and tumor extent difficult to detect, resulting in higher recurrence rates and more aggressive local tissue destruction compared to nodular or superficial BCC. 1, 2

Histologic Characteristics

• Infiltrative BCC is defined by irregular strands and nests of basaloid cells that infiltrate through the dermis in a non-sclerosing pattern, distinguishing it from morpheaform (sclerosing) BCC despite both being aggressive subtypes 3
• The tumor grows through irregular subclinical finger-like outgrowths that remain contiguous with the main tumor mass, extending far beyond what is clinically visible 1, 2
• Infiltrative BCC frequently shows deeper invasion into reticular dermis and subcutaneous fat, with significantly greater depth of invasion compared to nodular BCC of similar clinical size 4
• This subtype may demonstrate perineural or perivascular invasion, features associated with the most aggressive tumor behavior 1

Clinical Presentation

• Infiltrative BCC typically appears as an amelanotic hypopigmented plaque or papule, most commonly on the head and neck region 5
• On dermoscopic examination, infiltrative BCC displays ulceration, arborizing and fine superficial telangiectasia, and shiny white structures 5
• The clinical appearance is deceptively small—the visible lesion significantly underestimates the true extent of tumor spread, making clinical margin assessment unreliable 1, 4

Risk Classification

• The NCCN and American Academy of Dermatology classify infiltrative BCC as high-risk based on histologic subtype alone, regardless of tumor size or anatomic location 1, 2, 6
• This classification places infiltrative BCC in the same aggressive category as micronodular, morpheaform (sclerosing), and basosquamous variants 1
• Additional compounding high-risk features include location in Area H (central face, eyelids, eyebrows, periorbital, nose, lips, chin, mandible, preauricular and postauricular skin, temple, ear, genitalia, hands, feet), poorly defined clinical margins, recurrent disease, perineural invasion, and immunosuppression 2, 6

Diagnostic Approach

• Punch biopsy or shave biopsy must extend deep into the reticular dermis to detect infiltrative components, as superficial biopsies frequently miss the infiltrative pattern present only at deeper advancing margins 2, 6
• When recurrent tumor, deep invasion, or aggressive features are suspected, obtain multiple scouting biopsies or more extensive tissue resection 2
• Superficial tangential biopsies should never be performed for suspected BCC, as they will miss aggressive subtypes in up to 30% of cases 6

Treatment Implications

• Mohs micrographic surgery is the treatment of choice for infiltrative BCC, achieving 5-year disease-free rates exceeding 98% 2, 6
• Infiltrative BCC requires significantly more surgical stages for complete tumor removal compared to nodular BCC—the number of stages, width of tissue excision, and depth of defect are all statistically significantly greater 4
• Standard surgical excision with predetermined margins results in higher incomplete excision rates because the subclinical tumor extension is wider and deeper than anticipated 1, 4
• Radiation therapy may only be considered when surgery is contraindicated or refused by the patient, but recurrence rates are substantially higher than with surgical excision 2

Clinical Behavior and Prognosis

• Infiltrative BCC is significantly more destructive and difficult to eradicate than nodular BCC of similar clinical size 3, 4
• The tumor's covert invasion pattern—growing through irregular subclinical extensions—makes it more likely to recur after standard excision with fixed margins 4
• Recurrent infiltrative BCC carries even higher risk of further recurrence and requires Mohs surgery for optimal outcomes 1
• Metastasis remains extremely rare even with infiltrative BCC, but morbidity results from extensive local tissue invasion and destruction, particularly on the face, head, and neck 1

Important Caveat

• A focal infiltrative pattern seen in re-excision specimens at the site of previous biopsy may represent scar-induced changes rather than true aggressive-growth BCC, and these cases appear to have a more benign clinical course with lower recurrence rates after simple re-excision 7
• This scar-induced infiltrative pattern occurs in less than 5% of re-excision specimens and should be distinguished from primary infiltrative BCC by noting its focal nature and location within the biopsy scar 7