Massive solitary liver metastasis from a locally recurrent basal cell carcinoma treated with stereotactic body radiotherapy: a rare manifestation of a common disease

Introduction: Metastatic basal cell carcinoma (mBCC) is a rare but aggressive evolution of BCC, comprising only 0.0028-0.55% of cases.Despite novel therapies, outcomes remain poor.Liver metastases from BCC are exceedingly rare, underreported, and complex to manage.While stereotactic body radiotherapy (SBRT) is widely used for oligometastatic disease in other solid tumors, its role in mBCC remains unexplored.We present a case of liver-directed SBRT in mBCC, highlighting treatment response and associated challenges.Case Presentation: A 64-year-old man with recurrent basaloid-type BCC of the right neck had a massive (~15cm) liver metastasis identified following treatment for a local recurrence.It was initially mischaracterized as a hemangioma, but following interval growth and hepatic cancer pain, a biopsy confirmed mBCC with PTCH1 and TP53 mutations.He had limited response on hedgehog pathway inhibitor therapy and due to limited treatment options, he underwent liver SBRT (27.5 Gy/5 fractions).Treatment was well tolerated, with minimal side effects and resolution of hepatic pain.At 5 months post-SBRT, imaging showed partial response of the treated target; by 6 months the lesion began slowly progressing again.Systemic therapy was changed to cemiplimab and as of 11 months post-SBRT the lesion was once again stable with no other sites of disease.Despite the mixed response following multiple therapies, the patient had well-controlled hepatic pain for 9 months post-SBRT Conclusion: Liver metastases from mBCC are a rare manifestation of a common cancer that may be missed as they are unexpected.Evidence for metastasis-directed treatment in mBBC is limited, however, SBRT can provide a transient benefit even in large metastases, and further investigation is warranted.