This paper examines the reception of cell theory in the field of French anatomical pathology. This reception is studied under the lens of the concept of the cancer cell, which was developed in Paris in the 1840s. In the medical field, cell theory was quickly accessible, understood, and discussed. In the wake of research by Hermann Lebert, the cancer cell concept was supported by a wealth of high-quality microscopic observations. The concept was constructed in opposition to cell theory, which appears retrospectively paradoxical and surprising. Indeed, the biological atomism inherent in cell theory, according to which the cell is the elementary unit of all organs of living bodies, appeared at the time incompatible with the possible existence of pathological cells without equivalent in healthy tissues. Thus, the postulate of atomism was used as an argument by Parisian clinicians who denied the value of the cancer cell. This study shows that at least in the field of anatomical pathology, cell theory did not directly result from the use of the microscope but was actually hindered by it.