Basal Cell Carcinoma

Etiology

The principal etiologic factor in BCC development is exposure to ultraviolet (UV) radiation, particularly UVB wavelengths, although UVA also contributes.[3] Meta-analyses confirm a significantly higher incidence among outdoor workers, with risk increasing at lower latitudes.[4] Among White individuals, Fitzpatrick skin type is a strong predictor, with types I and II carrying the greatest susceptibility.

Cumulative UV dose alone does account for BCC risk; exposure timing and intensity, especially during childhood and adolescence, are critical determinants. Additional contributors include recreational sunlight exposure, blistering sunburns, indoor tanning, and certain phototherapies (particularly high-dose Psoralen plus UVA [PUVA]).[5] Notably, up to 20% of BCCs arise on non–sun–exposed sites, implicating additional risk factors such as prior ionizing radiation, arsenic exposure, immunosuppression, and inherited syndromes (eg, xeroderma pigmentosum, basal cell nevus syndrome, Bazex–Dupré–Christol syndrome, and Rombo syndrome).[6] There is no proven link between diet and BCC, and while some studies ' results suggest smoking may modestly increase risk in women, the evidence remains inconsistent.[7]

Epidemiology

BCC is the most common malignancy in humans, and its incidence continues to rise globally. Over the past 30 years, reported BCC incidence rates have increased by an estimated 20% to 80%. In the United States, approximately 5.4 million cases of basal and squamous cell carcinomas (SCCs) are diagnosed annually, affecting about 3.3 million individuals.[8]

Risk Factors

BCC arises from environmental, genetic, and host-related risk factors. The most significant contributor is UV radiation exposure, though additional risks include the following:

• Age: The risk increases with advancing age, with the median diagnosis occurring at approximately 68 years.
• Gender: Men have a higher incidence of BCC than women, particularly in older age groups.
• Ethnicity: White individuals have a higher lifetime risk compared to other racial groups.
• UV exposure: Chronic exposure to UV radiation is BCC's primary environmental driver.
• Previous skin cancer: A prior diagnosis of BCC or SCC significantly elevates the likelihood of developing subsequent BCCs.

Prognosis and Mortality

BCC is typically a slow-growing tumor with very low metastatic potential. Mortality is rare and occurs most often in immunocompromised individuals. The estimated age-adjusted mortality rate for BCC is 0.12 per 100,000 individuals.[9]

Metastasis

Metastatic BCC is exceedingly rare, with an estimated incidence ranging from 0.0028% to 0.55%.[10] When metastasis occurs, it often involves regional lymph nodes, bone, lungs, and skin.

Pathophysiology

Chronic sun exposure is among the most critical risk factors for developing BCC. There is typically a latency period of 15 to 20 years between UV damage and the clinical onset of BCC.[11] UV radiation promotes BCC formation through direct and indirect DNA damage and immune suppression. UVB directly damages DNA and RNA, producing characteristic C→T or CC→TT transition mutations. UVA generates reactive oxygen species through melanin absorption, resulting in indirect DNA damage. Ultraviolet exposure also causes dose-dependent suppression of the cutaneous immune system, impairing immune surveillance against emerging skin cancer.

Genetic Alterations in BCC

The pathogenesis of BCC is strongly linked to mutations in the Hedgehog (Hh) signaling pathway and other tumor suppressor genes:[12]

• PTCH1 mutations: Inactivating mutations in the PTCH1 gene are present in approximately 70% to 90% of BCCs. 
• SMO mutations: Activating mutations in the SMO gene occur in approximately 10% to 20% of BCCs, resulting in aberrant Hh pathway activation.[12]
• TP53 mutations: Mutations in the TP53 gene are the second most common genetic alterations in BCCs, found in approximately 44% to 65% of cases. 
• CDKN2A mutations: Mutations in the CDKN2A gene are less common in sporadic BCCs, and variable frequencies have been reported across studies.

Histopathology

The hallmark histopathologic feature of BCCs is the presence of islands or nests of basaloid cells, characterized by peripheral palisading of nuclei and a more disorganized arrangement within the tumor centers. These small pleomorphic cells typically have basophilic nuclei, no discernible nucleoli, and scant cytoplasm. A retraction artifact (clefting) between the tumor and surrounding stroma is commonly observed in paraffin-embedded sections. Additional findings may include mucin deposition within and around the tumor, as well as the presence of mitotic figures. Perineural growth, also known as perineural invasion, can indicate aggressive disease.

The histologic differential diagnosis of BCC includes trichoepithelioma and trichoblastoma. Multiple morphological subtypes of BCC have been described, including nodular (solid), micronodular, superficial, cystic, infiltrating, infundibulocystic, pigmented, adenoid, sclerosing, metatypical, basosquamous, and fibroepitheliomatous (see Image. Pigmented Basal Cell Carcinoma). Mixed patterns of these subtypes are also common.

• The superficial subtype features multiple, small basaloid cell buds descending from the epidermis, without dermal invasion.[13][14]
• The nodular variant, which accounts for most cases, consists of islands of basaloid cells with peripheral palisading and a haphazard arrangement of central cells. Ulceration may occur in larger lesions (see Image. Basal Cell Carcinoma, Nodular).[13][14] 
• The micronodular subtype resembles nodular BCC but is composed of numerous small nodules. The micronodular type has a significantly higher risk of local recurrence than the solid type (see Image. Micronodular Basal Cell Carcinoma).[13][14]
• The sclerosing (morpheaform) subtype exhibits spiky strands of basaloid cells infiltrating the dermis within a dense fibrous stroma. The histologic differential diagnosis includes microcystic adnexal carcinoma, desmoplastic trichoepithelioma, and metastatic cancer. When most tumor nests show spiky projections, the tumor may invade deeply, an infiltrative BCC (see Image. Basal Cell Carcinoma, Morpheaform).[14]
• The pigmented BCC results from the presence of melanocytes and melanin interspersed among tumor cells, occurring most commonly in superficial, micronodular, or follicular variants (see Image. Basal Cell Cancer).
• The infundibulocystic variant is uncommon and often found on the face, appearing as a small, well-circumscribed tumor composed of anastomosing nests of basaloid cells with minimal stroma. Numerous small infundibular cyst-like structures contain keratinous material and occasional melanin.
• Basosquamous or metatypical BCC shows features of both BCC and SCC. The exact nature of this lesion is controversial; however, the term is generally applied to a rare type of BCC composed of nests and strands of basaloid cells that mature into larger, paler cells lacking peripheral palisading.
• Fibroepithelioma of Pinkus presents as a soft nodular lesion resembling a fibroma or papilloma, commonly on the lower back. These comprise anastomosing strands and aggregates of basaloid cells within a fibrous stroma (see Image. Basal Cell Carcinoma, Fibroepithelioma of Pinkus).[13][14]

History and Physical

Many clinical variants of BCC exist, but the most recognized types are superficial, nodular, and morpheaform BCC. Nodular BCC is the most prevalent (see Image. Nodulocystic Basal Cell Carcinoma). BCC typically presents as a shiny, pink- or flesh-colored papule or nodule with surface telangiectasia. As the lesion enlarges, ulceration may develop, producing the characteristic rolled or "rodent ulcer" borders. Nodular BCC often arises on the face, especially the nose, cheeks, forehead, nasolabial folds, and eyelids. Patients frequently report a history of crusting and recurrent bleeding, prompting medical evaluation. Pigmented nodular BCC is more common in individuals with darker skin tones.

Superficial BCCs are pink to red, and scaly macules or patches may contain telangiectasia (see Image. Superficial Basal Cell Carcinoma). They have a predilection for the shoulders, chest, or back, and multiple lesions may be present. Pigmented variants can also occur (see Image. Pigmented Basal Cell Carcinoma of Temple). Clinically, superficial BCC can resemble inflammatory dermatoses such as eczema or psoriasis; thus, persistent, erythematous, scaly plaques should prompt consideration of superficial BCC. Over time, areas of superficial BCC can evolve into nodular BCC.

The morpheaform subtype is another common clinical variant of BCC. These tumors frequently present as white or flesh-colored with induration and poorly defined borders, often resembling a scar or plaque of morphea. The surface is typically smooth, although it may be crusted with underlying erosions, ulcerations, or superimposed papules, which telangiectasias can sometimes accompany. Morpheaform BCC generally exhibits a more aggressive biologic behavior, with a tendency for extensive local tissue destruction.

Evaluation

A skin biopsy is necessary for definitive diagnosis of BCC. Acceptable techniques include shave, punch, or excisional biopsy, with attention to sampling a portion of the dermis to distinguish superficial from more invasive histologic subtypes. Punch and shave biopsies are about 80% accurate in identifying the various BCC subtypes.[15]

A qualified clinician should perform a comprehensive skin examination, as individuals with 1 skin cancer frequently have additional cancers or precancerous lesions and remain at an elevated risk for other cutaneous malignancies. Photographic or digital documentation of lesion sites is recommended. Clinicians should maintain a low threshold for biopsy in these patients. Preoperative imaging may be warranted when there is concern for involvement of the parotid gland, muscle, deep soft tissue, orbit, bone, or perineural invasion. Patients with a history of BCC require long-term, often lifelong follow-up, particularly those with multiple or high-risk tumors.

Dermoscopy is a valuable tool for experienced clinicians in diagnosing pigmented and nonpigmented BCCs. The hallmark feature is the presence of well-focused arborizing vessels. Additional findings include multiple blue-gray globules, leaf-like structures, large blue-gray ovoid nests, and spoke-wheel areas. BCC lacks the pigment network typically seen in melanocytic lesions. 

Treatment / Management

Treatment planning for BCCs depends on patient factors (such as age and gender) and tumor characteristics (including site, size, and histologic subtype). No single approach is universally appropriate for all patients or lesions. A biopsy should be obtained in all suspected cases to confirm the diagnosis and guide management. The primary goals of therapy are: (1) complete tumor removal to prevent recurrence, (2) preservation or restoration of function, and (3) achievement of the best possible cosmetic outcome.[16](A1)

The management of BCC typically involves surgical intervention, although certain cases may be treated with medical or radiation therapies. Surgical approaches include Mohs micrographic surgery (MMS), standard surgical excision, electrodessication and curettage (EDC), and cryosurgery. Nonsurgical options encompass radiation therapy, photodynamic therapy, topical therapies, and systemic medications such as vismodegib. Reported recurrence rates for primary BCC vary by modality: MMS, 1.0%; surgical excision, 10.1%; EDC, 7.7%; radiation therapy, 8.7%; and cryosurgery, 7.5%.[17][18]

Mohs surgery provides the best long-term cure rate of all treatment modalities for BCC and is considered the gold standard for managing high-risk BCCs and recurrent BCCs because of its high cure rate and tissue-sparing benefit. The high cure rate stems from examining 100% of surgical margins compared to standard vertical sectioning, which assesses less than 1% of peripheral and deep margins. By removing thin layers of tissue only from areas with positive tumor margins, MMS minimizes wound size and maximizes the likelihood of a favorable cosmetic outcome. 

Postoperative pathologic analysis with permanent sections is standard following surgical excision. A 4 mm margin is typically sufficient for well-circumscribed tumors smaller than 2 cm in diameter. For facial lesions, narrow-margin excision is often inadequate for complete tumor removal. EDC is frequently used for low-risk BCCs, with reported cure rates of 97% to 98% when tumors do not extend into the deep dermis. While EDC is the least expensive and fastest treatment option, wounds heal by second intention, often leaving a white, atrophic scar that may be cosmetically unfavorable. 

Radiation therapy is a primary treatment option for BCC or SCC when surgery is contraindicated, and it also serves as an adjuvant treatment in cases where further surgery could risk damage to major nerves or other vital structures, or when perineural invasion is present. The disadvantages of radiation therapy are higher cost, potential for suboptimal cosmetic outcomes, lengthy treatment courses (typically 15-30 sessions), and an increased risk for secondary skin cancers. Unlike surgical scars, which often improve over time, radiation-induced scars may worsen with age. Radiation is relatively contraindicated in those with connective tissue disorders. The NCCN explicitly notes that patients with scleroderma are at elevated risk of severe radiation-induced fibrosis, necrosis, and poor wound healing, making RT a poor choice even when technically feasible.[19](B3)

Cryosurgery is an option for treating low-risk BCCs. The procedure involves the controlled application of liquid nitrogen to the clinically visible tumor and a small margin of surrounding normal-appearing skin. A temperature probe can be inserted at the lateral tumor margin, with the tip positioned obliquely beneath the tumor. Liquid nitrogen is applied until the temperature reaches -60 °C, although temperature monitoring is seldom employed in practice. Cryosurgery is a relatively quick and minimally invasive procedure, making it suitable for patients who wish to avoid traditional surgery. However, the treated area often becomes painful and swollen after thawing, and potential complications include hypertrophic scarring and permanent pigment alteration.

Topical therapy is an additional treatment option for BCC. Topical 5-fluorouracil (5-FU) and imiquimod 5% cream are approved by the Food and Drug Administration (FDA) to manage superficial BCC. especially when the lesion is <2 cm, well-demarcated, and confined to the superficial dermis These agents are useful options in patients with multiple superficial BCCs and in those who are poor surgical candidates. Local application-site reactions are common and may include erythema, pruritus, pain, edema, hypopigmentation, hyperpigmentation, crusting, bleeding, and erosions. A significant limitation of topical therapy is the lack of complete tumor clearance and histologic confirmation.

A more recent option for patients with advanced or metastatic BCC not amenable to conventional therapies is treatment with hedgehog pathway inhibitors (HHI). The FDA approved vismodegib in 2012, followed by sonidegib, indicated for locally advanced lesions that cannot be treated with surgery or radiation.[20] Unlike immunotherapy, HHIs do not rely on immune activation and have not been associated with increased transplant rejection risk. They are considered appropriate for use in solid organ transplant recipients with locally advanced BCC.[21] The adverse effects may result in discontinuation in up to 55% of patients. The most commonly reported adverse effects included nausea, dysgeusia, muscle spasm, alopecia, weight loss, diarrhea, and fatigue. For those who respond well to HHI but stop due to side effects, a drug holiday and restart of the same drug class is a reasonable approach. Cemiplimab is a monoclonal antibody immune checkpoint inhibitor that is indicated as a second-line treatment for locally advanced or metastatic basal cell carcinoma.[22] In specific populations, such as immunosuppressed individuals, older adults, and those with poor baseline functional status, surgery may not be the optimal option. For individuals with metastatic, advanced, recalcitrant, or cosmetically sensitive disease, nonsurgical management may be a preferred alternative.[16](A1)

Differential Diagnosis

The differential diagnosis of BCC includes adnexal tumors with follicular, sweat gland, or sebaceous differentiation and specific subtypes of squamous cell carcinoma (SCC). Nodular BCC may resemble trichoblastoma or trichoepithelioma, while superficial BCC may mimic inflammatory dermatoses such as psoriasis or eczema. Morpheaform BCC may be mistaken for a scar or a plaque of morphea. In such cases, histopathological examination is essential to confirm the diagnosis.   

Pertinent Studies and Ongoing Trials

Ongoing clinical trials in BCC are exploring novel therapeutic approaches beyond standard surgical management. Investigational studies include the use of Hh pathway inhibitors, such as vismodegib, in combination with surgery, topical agents like patidegib for Gorlin syndrome, and immune checkpoint inhibitors, such as cemiplimab, for advanced or metastatic BCC following prior Hh inhibitor therapy.[23][24] Prophylaxis for syndromic basal cell includes systemic nicotinamide.[25] Additional trials are examining the safety and efficacy of oncolytic virus therapy (RP1) in patients with advanced cutaneous malignancies, including those with solid organ transplants, as well as photodynamic therapy using BF-200 ALA and Ameluz with the BF-RhodoLED lamp.[26] These studies, designed as randomized controlled, open-label, or multicenter trials, aim to improve treatment efficacy, reduce adverse events, and expand therapeutic options for patients with locally advanced, recurrent, or treatment-resistant BCC. Participation in these trials provides early access to emerging therapies and advances clinical knowledge in managing BCC.

Staging

BCC is primarily staged based on tumor size, location, histologic subtype, and high-risk features. Unlike many other malignancies, formal tumor, node, metastasis (TNM) staging is less commonly applied for BCC due to its very low metastatic potential. High-risk features include tumor diameter greater than 2 cm, location on the central face, ears, or scalp, poorly defined borders, recurrent tumors, aggressive histologic subtypes (morpheaform, infiltrative, micronodular, or basosquamous), and perineural invasion. While regional or distant metastases are exceedingly rare, staging may be considered in advanced or high-risk cases to guide management. Risk stratification informs treatment decisions, including selecting MMS, standard excision with appropriate margins, or adjunctive therapies such as radiation or systemic Hh pathway inhibitors for locally advanced or inoperable disease.

Prognosis

BCC is rarely associated with a fatal outcome. Prognosis is primarily determined by the risk of recurrence after initial therapy, which depends on the tumor's location and its clinical and histopathological features.    

• Good prognosis:
  • Primary superficial BCC
  • Primary nodular BCC <1cm in an intermediate-risk location or,
  • <2 cm in a low-risk location
• Intermediate prognosis:
  • Recurrent superficial BCC
  • Nodular BCC <1 cm in a high-risk location or,
  • <2 cm in an intermediate-risk location or,
  • >2cm in a low-risk location
• Poor prognosis:
  • Nodular BCC >1 cm in a high-risk location (high risk of recurrence)
  • Morpheaform, infiltrative, or other histologically aggressive subtypes (very high recurrence risk)
  • Recurrent tumors (except superficial BCC), which also carry a very high risk of recurrence

Complications

Treatment of BCC is generally effective but may be associated with complications that vary depending on the treatment modality. The likelihood and severity of these complications depend on factors such as tumor location, size, patient comorbidities, and the specific therapeutic approach chosen. Surgical interventions, including MMS and standard excision, carry risks such as bleeding, infection, delayed wound healing, scarring, and cosmetic or functional deficits, particularly in anatomically sensitive areas such as the face. These risks are generally low but can significantly impact quality of life when lesions occur in cosmetically or functionally critical areas.

Nonsurgical therapies, including radiation, photodynamic therapy, topical agents, and systemic Hh pathway inhibitors (eg, vismodegib), can lead to localized skin reactions, pain, erythema, edema, alopecia, taste disturbances, muscle cramps, and gastrointestinal symptoms. Rarely, systemic therapy may cause more severe adverse effects, such as teratogenicity, weight loss, or fatigue, underscoring the need for careful patient selection, monitoring, and interprofessional management to optimize outcomes and minimize morbidity.