孤癌入髓
[gū ái rù suĭ]
Bone-deep solitariness or Loneliness. It paints an intense image of profound loneliness, indicating severe mental states like isolation or detachment akin to illness deeply ingrained into one's psyche ('孤癌' can imply a form of metaphorical ‘lonely cancer’), making it hard for such individuals to engage socially.