AUSTIN, Texas — Given that existing adjuvant radiation guidelines for high-risk cutaneous squamous cell carcinoma (cSCC) are inconsistent and based on small, heterogeneous studies, an expert committee laid out recommendations for when to consider radiation after surgery, according to a study presented at the American College of Mohs Surgery (ACMS) Annual Meeting 2026.

“This Delphi study provides an expert consensus-based framework to standardize adjuvant radiation for known negative high-risk cutaneous squamous cell,” Jacqueline S. Stevens, MD, PhD, Mohs Micrographic Surgery and Cutaneous Oncology Fellow at Brigham and Women’s Hospital and Dana-Farber Cancer Institute in Boston, told attendees. “These results can be used to inform future guidelines and radiation utilization,” she added.

While surgery works very well most of the time for high-risk cSCC, certain tumors continue to carry significant risk, she noted.

“Adjuvant radiation therapy has been a mainstay for treatment intensification, but there’s variability in clinical guidelines with a wide range of recommendations that incorporate different factors,” Stevens said. Each of these factors carries different risks, and data underpinning the guidelines are sparse, often extrapolated from head and neck cancer and then applied to cSCC, she said. Even those are typically small, heterogeneous, retrospective studies, she added.

“Existing guidelines don’t align, contributing to wide practice variations, and while ideally we would like to have a prospective study to look at the benefit of adjuvant radiation, these studies take a long time and have been challenging to conduct,” Stevens said.

She and her colleagues used the Delphi method to come up with consensus recommendations for adjuvant radiation for cSCC. The 35 experts included 15 radiation oncologists, nine dermatologists/Mohs surgeons, seven medical oncologists, three head and neck surgeons, and one surgical oncologist, all from diverse settings throughout the US. 

In the first round of surveys, conducted from July through August 2025, the experts considered 16 questions about cSCC tumors and patient indications for adjuvant radiation therapy and came to a consensus of at least 80% concordance on 11 questions. 

“Between rounds, panelists reviewed panel responses, summary tables, and additional evidence, and then we incorporated free response questions to help guide the next round,” Stevens explained.

The second round in September and October 2025 involved 22 questions, further refining tumor and patient indications and, for radiation oncologists, an examination of adjuvant radiation therapy protocols. Consensus was reached for 17 questions. The final round in November and December 2025 included 21 questions and explored the role of immunosuppression and systemic therapy, with consensus reached on eight questions. 

Stevens reviewed several examples of the consensus recommendations reached. 

“All panelists agreed that for a tumor with gross or microscopic positive margins, and when further surgery is not possible, we should consider adjuvant radiation,” she said. “The panel converged around risk threshold following clear margin surgery,” so adjuvant radiation would also be recommended, with 86%-100% consensus, for tumors with at least three risk factors, which include a tumor diameter of 2 cm or greater, invasion beyond fat, a large-caliber perineural invasion, and poor differentiation.

Other cases where adjuvant radiation therapy should be considered, with consensus of 77%-86%, are tumors with an estimated 5-year risk for local recurrence or nodal metastasis exceeding 20%, tumors with perineural invasion of at least 0.1 mm plus one other risk factor, and tumors with clinical nerve invasion or gross cortical bone, marrow, or skull bone invasion.

“Importantly, the panel’s use of risk thresholds highlights our ability to consider risk factors as they apply to a threshold in order to do personalized decision-making for our patients,” Stevens said.

Most panelists (82%) would consider a patient’s immune status and recommend adjuvant radiation for immunosuppressed patients (77%) but would defer radiation for patients with an ECOG Performance Status of 4 (91%) or for nonhealed wounds (83%) or exposed bone (86%), she reported.

“Following neoadjuvant immunotherapy and surgery, the panel agreed that the pathologic response of the tumor should guide treatment,” with 77% agreement, Stevens continued. Adjuvant radiation is not recommended in cases of a complete pathologic response (97%), but no consensus was reached for cases of a major pathologic response (34% would recommend it). Nearly all panelists would recommend radiation for no pathologic response (97%), and most would do so for a partial response (74%).

“This aligns with current trials that are looking at using the pathologic response to guide adjuvant treatment,” Stevens said.

Radiation oncologists all agreed that the optimal window for starting adjuvant radiation is 4-8 weeks, with 4 months being too late when balancing urgency to start with wound healing concerns. The radiation oncologists also made recommendations about specific radiation treatment protocols and doses, including agreeing that superficial radiation and brachytherapy would be inappropriate (93%) for high-risk cSCC.

“This highlights that, while these might be appropriate in low-risk nonmelanoma skin cancer, we really should not be considering these for high-risk tumors for which they haven’t been studied in the adjuvant setting,” Steven said. 

The study’s limitations included reliance on expert opinion instead of patient-level outcomes from primarily academic panelists.

Nevertheless, the recommendation was in line with what Jordan Lim, MB ChB, BAO, assistant professor of dermatology and board-certified Mohs surgeon at Emory University in Atlanta, would expect, she told Medscape Medical News.

“I thought the study was really beautifully done,” said Lim, who was not involved in the research. She acknowledged that a consensus statement is “always the beginning,” with actual data and studies still important to collect, “but we have to start somewhere.” 

Lim particularly appreciated seeing the 20% risk threshold for local recurrence or nodal metastasis.

“A lot of us sitting together were saying, we use this risk stratification tool, which is fantastic, but when we see those local recurrence numbers, we don’t know what to do with them,” Lim said. “So that was a big takeaway for me that I might start implementing.”

Stevens and Lim reported having no disclosures. No external funding for the study was noted.

Tara Haelle is a science/health journalist based in Dallas.