Hidden Tumor Spread: Mapping Biopsies Guide Surgery for Recurrent Skin Cancer

Basal cell carcinoma is the most common form of skin cancer, and in most patients it can be effectively controlled with local treatment. Yet a report from dermatologists at Kindai University Hospital in Osaka, Japan, published in the Journal of Cutaneous Immunology and Allergy, shows how a single recurrent case can expose the limits of conventional surgical planning. The letter to the editor describes an elderly man in his 80s whose basal cell carcinoma returned on the posterior neck a decade after apparently complete excision, and whose tumor exhibited an unusual combination of deep nodular formation and superficial lateral microextension that made its boundaries nearly impossible to define clinically.

The patient’s history is central to the case. Ten years earlier, he had undergone complete surgical excision of a basal cell carcinoma at another hospital with a 5-millimeter margin extending to the level of the subcutaneous tissue. Histopathological examination at that time had judged the surgical margins to be negative. Approximately one year before presentation at Kindai University Hospital, however, an erythematous plaque appeared at the same site and gradually enlarged. When the tumor was excised with what appeared to be adequate margins, the lesion was followed without further treatment, and it eventually recurred after a long interval.

At presentation, the clinical picture was deceptively simple. An ill-defined erythematous plaque measuring approximately 7 centimeters in diameter extended from the occipital region to the posterior neck, accompanied by a palpable subcutaneous nodule. Computed tomography showed a corresponding high-density lesion without lymph node enlargement or distant metastasis, and a skin biopsy confirmed recurrent basal cell carcinoma. The tumor was excised with a 1-centimeter margin, and the defect was reconstructed using a full-thickness skin graft.

Histopathological examination of the excised specimen revealed the technical crux of the case: infiltrative basal cell carcinoma with deep invasion and superficial lateral microextension extending beyond the clinically apparent lesion. The lateral margin was positive, and the minimum distance between the tumor and the deep surgical margin was only 0.5 millimeters. Infiltrative basal cell carcinoma is one of several histological subtypes in which tumor nests infiltrate in cord-like or micronodular patterns, which often obscure tumor boundaries both clinically and histopathologically.

Examination of the primary excision specimen showed that tumor nests were distributed predominantly within the subcutaneous tissue, with only limited continuity with the epidermis. Such a distribution may be difficult to recognize clinically as a superficial lesion and may lead to underestimation of tumor extent at the time of initial excision. Because the surgical margins had been judged negative, the lesion was followed without additional treatment, and the tumor eventually recurred after a long interval. The report suggests that this pattern of deep subcutaneous growth with limited epidermal continuity may explain why the tumor extent was difficult to appreciate clinically and why conventional margin determination based on surface findings was insufficient.

In the recurrent lesion, the tumor formed a nodular mass within the deeper subcutaneous tissue, suggesting a more aggressive growth pattern. At the same time, the tumor retained subtle lateral microextension within the superficial subcutaneous layer beyond the deep nodular component, making accurate margin determination difficult. Changes in skin coloration and a palpable subcutaneous nodule were used as clinical landmarks for estimating the tumor boundary; however, margin determination based solely on palpation was insufficient to capture the lateral tumor spread within the superficial subcutaneous layer.

To address this challenge, the surgical team employed a mapping biopsy strategy. Three weeks after the initial excision, mapping biopsies were performed at 13 sites to assess lateral tumor spread. The biopsies extended approximately 5 millimeters in depth to include the superficial subcutaneous tissue. Approximately 6 weeks later, additional excision was performed, with the resection boundary determined by connecting tumor-negative mapping biopsy sites. Histopathological examination confirmed complete tumor clearance, and no recurrence was observed at 6 months after the final excision.

Mohs micrographic surgery, a technique in which tumor is removed layer by layer with immediate microscopic examination of margins, is recommended for high-risk basal cell carcinoma. However, its availability varies among institutions. In retrospect, given the difficulty in clinically determining the tumor extent in this case, the authors suggest that temporary coverage with artificial dermis at the initial excision, followed by definitive reconstruction after histopathological confirmation of clear margins, might have been a reasonable alternative approach. In situations where Mohs surgery is not feasible, mapping biopsy may be useful for assessing tumor extent and guiding appropriate surgical margins.

The case underscores a broader principle in skin cancer surgery: histological subtype matters. In certain subtypes, including infiltrative basal cell carcinoma, tumor nests infiltrate in cord-like or micronodular patterns that often obscure tumor boundaries both clinically and histopathologically. It has also been reported that recurrent lesions may exhibit atypical patterns of tumor spread. The combination of deep nodular formation and superficial lateral microextension observed here represents one such atypical pattern, in which the clinically visible lesion substantially underestimated the true tumor extent in multiple directions.

For clinicians managing high-risk or recurrent basal cell carcinoma, the report offers a practical message. When tumor boundaries cannot be reliably determined clinically, particularly in infiltrative subtypes or recurrent lesions, surgeons should consider strategies that verify margins histopathologically before definitive reconstruction. Whether through Mohs micrographic surgery where available, temporary artificial dermis coverage pending margin confirmation, or mapping biopsy to delineate lateral spread, the goal remains the same: ensuring complete tumor clearance while avoiding unnecessary sacrifice of healthy tissue. In this case, a staged approach combining initial excision, systematic mapping biopsies, and definitive second excision achieved complete tumor clearance with no recurrence at 6 months.

Subject of Research: Recurrent infiltrative basal cell carcinoma with deep nodular formation and superficial lateral microextension

Article Title: Recurrent infiltrative basal cell carcinoma with deep nodular formation and superficial lateral microextension

Article References: Maeda, M., Yamamura, Y., Fujii, K., Nishimura, K., Usui, S., & Otsuka, A. (2026). Recurrent infiltrative basal cell carcinoma with deep nodular formation and superficial lateral microextension. Journal of Cutaneous Immunology and Allergy, 9, Article 17511. https://doi.org/10.3389/jcia.2026.17511

Image Credits: AI Generated

DOI: 10.3389/jcia.2026.17511

Keywords: basal cell carcinoma, skin cancer, tumor recurrence, mapping biopsy, surgical margins, infiltrative growth, Mohs surgery, dermatology, case report, subcutaneous invasion, Recurrent, infiltrative