Associate Professor John Frew
In a decade-long analysis of more than 1,000 scalp cancers treated with Mohs surgery, Sydney researchers have found distinct differences between basal and squamous cell carcinomas, offering clinicians new clues for diagnosis and treatment.
The investigators from The Skin Hospital, Sydney, say the study helps fill a long-standing evidence gap in scalp cancers managed with Mohs surgery, which suffers from ‘a paucity’ of research data.
The retrospective review published in the Australasian College of Dermatologists [link here] examined 1,177 scalp keratinocyte carcinomas (KCs) treated with Mohs micrographic surgery (MMS) between 2012 and 2022. The cohort included 948 basal cell carcinomas (80.5%) and 229 squamous cell carcinomas (19.5%).
Patients with squamous cell carcinoma were significantly older, with a median age of 73 years compared to 60 for basal cell carcinoma, and SCCs were markedly more common in men (79% vs 48%), reported dermatologist Associate Professor John Frew and colleagues.
They noted the scalp had long been viewed as a high-risk site for skin cancer, with previous studies suggesting poorer prognoses in this region, possibly due to delayed diagnosis, larger lesions, growth beyond visible borders, peripheral nerve invasion and in-transit metastases.
Coupled with that it was also a surgically challenging area with high vascularity and low laxity, adding complexity to tumour clearance and reconstruction, the authors said.
On the other hand, their new analysis challenged that assumption, finding no evidence that the scalp itself predisposes to intrinsically aggressive disease.
“Our findings do not support previous suggestions where scalp KCs demonstrated an intrinsically aggressive behaviour,” the authors wrote. The number of Mohs stages required to achieve tumour clearance was similar between BCCs and SCCs (p = 0.12).
Notably though, they found that while BCCs were more likely overall to present with aggressive subtypes (58% vs 21% of SCCs), it was the aggressive SCCs that showed the greatest degree of subclinical spread (29.5% vs 16.4%).
“To our knowledge, this has not been previously described in the literature and deserves further attention for future research,” the team said.
Most tumours were located on the frontal (55%) and vertex (29%) scalp – regions with high cumulative ultraviolet exposure, particularly in men with reduced hair density. “The greater incidence of scalp KC in males has been hypothesised to be due to factors such as lower hair cover, hairstyles, androgenetic alopecia and occupational and recreational time spent outdoors,” the study said.
Primary closure was the most common repair method (55%), reflecting both earlier detection and growing surgical expertise among Mohs specialists.
“This trend may reflect increased MMS utilisation due to improvements in early detection and referral, in combination with greater surgical skill and experience,” the authors noted.
The researchers concluded that the data “provide insights into the characteristics and management of scalp KCs referred for MMS over a 10-year period at a centre housing the largest number of Mohs specialists in Australia,” adding that the findings “may help to better inform clinical practice and inspire further research in this area.”