noun
histologist
A specialist in histology, the study of the microscopic structure of tissues.
彼女は組織学者として、がん細胞の微細構造を研究している。
As a histologist, she studies the fine structure of cancer cells.
組織学 is the field of histology, while 組織学者 refers to a person who specializes in it.
Compound of 組織 (tissue, organization) + 学 (study) + 者 (person). The reading is straightforward on'yomi.