Rare lung cancer first discovered as a mass in the skull

What happened, in summary

A man in his 50s developed numbness and pain around his right upper lip, worsening headache on the right side, and altered facial sensation. MRI found a large mass involving the right skull base, sphenoid sinus, and nearby facial structures. The first concern was either a primary tumor in that area or spread from another organ.

Biopsy showed adenocarcinoma with intestinal features. The tumor was positive for CK7 and CDX2 and carried a KRAS G12C mutation. Review of the pathology together with chest imaging supported pulmonary enteric adenocarcinoma, a rare lung-cancer subtype that can resemble colorectal cancer. Disease was present in the right hilar region and had spread to the skull base and the right posterior acetabulum. The cancer was classified as Stage IV, T1cN0M1c.

Surgery could not remove the skull-base disease with clear margins. He received palliative radiation of 50 Gy in 20 treatments to the skull-base, masticatory-space, and nasal lesion. A second course of 30 Gy in 10 treatments was delivered to the right acetabulum.

Systemic treatment began with 4 cycles of carboplatin, pemetrexed, and pembrolizumab. He then continued pemetrexed and pembrolizumab every 21 days for 31 additional cycles, reaching 35 cycles in total.

The skull-base disease explained the facial numbness and headache. Radiation was delivered to both the skull-base region and the right acetabulum, followed by the prolonged systemic-treatment course. The cancer remained Stage IV because metastatic disease had involved the skull base and the right acetabulum.