Basal cell carcinoma (BCC) is the most common malignant skin tumour. The standard treatment is micrographically controlled surgery (MMS), which achieves high cure rates but requires considerable time and personnel. A key problem is the inadequate preoperative determination of tumour margins, which often leads to multiple cycles of excision.

The aim of this multicentre, prospective, randomised controlled intervention study is to evaluate line-field confocal optical coherence tomography (LC-OCT) for preoperative margin determination in BCC within the framework of MMS.

Research question:

Can preoperative LC-OCT-assisted margin marking increase the efficiency of MMS by reducing the number of excision cycles required without compromising oncological safety?

Methodology:

Approximately 290 patients with histologically confirmed BCC will be enrolled at five German centres and randomly assigned to either standard MMS or MMS with upstream LC-OCT margin determination. In the intervention group, the excision margin will be specifically extended if a tumour is detected in the LC-OCT.

Primary endpoint:

Number of MMS cycles required to achieve R0 resection.

Secondary endpoints:

Total duration of surgery, size of surgical defect, cosmetic outcome (POSAS), patient satisfaction and stress, sensitivity and specificity of LC-OCT compared to histopathology.

Significance:

The study addresses the clinical conflict of objectives between complete tumour removal and maximum tissue preservation. Successful implementation could optimise MMS through modern imaging, conserve surgical resources and improve patient care in the long term.

Basal cell carcinoma (BCC) is the most common type of skin cancer worldwide and occurs predominantly in fair-skinned populations. In Germany, approximately one in three individuals will develop BCC during their lifetime. Although BCC rarely metastasizes, it shows locally destructive growth with irregular, finger-like extensions into surrounding tissue, which can make complete surgical removal challenging. The majority of tumors arise in the sun-exposed head and neck region.

Micrographic surgery (Mohs micrographic surgery, MMS) represents the gold standard treatment for high-risk BCC, as it allows complete margin control and offers the highest cure rates. However, MMS is often time-consuming and resource-intensive because multiple sequential excision stages may be required until histopathology confirms complete tumor removal (R0 resection). Preoperative estimation of tumor margins is usually based on clinical examination and dermoscopy with a standard safety margin of 2-3 mm. This approach may be inaccurate, particularly in tumors with subclinical extension, which can lead either to unnecessarily large excisions or to residual tumor tissue requiring additional surgical stages.

Non-invasive imaging techniques have increasingly been investigated to improve the preoperative assessment of BCC margins. Optical coherence tomography (OCT) and the more recently developed line-field confocal optical coherence tomography (LC-OCT) allow high-resolution, real-time imaging of the skin. These technologies enable visualization of skin structures with near-histological resolution and can detect characteristic morphological features of BCC in vivo. Previous studies have demonstrated good diagnostic accuracy of OCT and LC-OCT for the detection and subtyping of BCC and suggest that these methods may also be useful for defining tumor margins before surgery.

In particular, LC-OCT combines the advantages of conventional OCT with the cellular resolution of confocal microscopy, allowing both vertical and horizontal imaging of the skin at high resolution. This enables detailed visualization of tumor architecture and potentially facilitates the detection of subclinical tumor extensions beyond the clinically visible borders.

The present multicenter randomized controlled study aims to evaluate whether LC-OCT-guided preoperative margin assessment can improve the efficiency of MMS. In the intervention group, the lateral tumor margins are examined preoperatively using LC-OCT. If tumor structures are detected at the planned resection margin, the surgical margin is extended accordingly before the first excision step. MMS is then performed according to the standard surgical protocol with histopathological examination of the margins. In centers where available, excised tissue may additionally be examined postoperatively using ex vivo LC-OCT or confocal microscopy to correlate imaging findings with histopathology.

The study investigates whether this image-guided approach can reduce the number of surgical stages required to achieve complete tumor removal, while maintaining oncological safety. By enabling more accurate preoperative mapping of tumor margins, LC-OCT-guided surgery may improve surgical planning and increase the likelihood of complete excision in the first stage of MMS. In addition, improved margin delineation could allow more tissue-sparing surgery, potentially leading to smaller surgical defects and better cosmetic outcomes.

Overall, this study evaluates the clinical utility of integrating LC-OCT into the surgical workflow of MMS. The results may provide evidence for a more efficient and resource-conserving surgical strategy in the treatment of basal cell carcinoma while maintaining the high oncological safety standards of micrographic surgery.

Inclusion Criteria:

• Adults (≥18 years) with basal cell carcinoma (BCC) scheduled for Mohs micrographic surgery (MMS),
• Diagnosis confirmed by dermoscopy and histopathology or optical coherence tomography (OCT),
• No limitation regarding tumor size or BCC subgroups.

Exclusion Criteria:

• Poor LC-OCT image quality,
• Incomplete adherence to the study protocol,
• Previous treatment of the BCC,
• Anatomical sites that are difficult to access with LC-OCT (e.g., inner ear, medial canthus of the eye).