<p>Whereas the size and shape of spheroids are routinely measured, information about their mechanical properties is often lacking. This study aimed to evaluate the role of atomic force microscopy in characterizing heterotypic cancer spheroids and their interaction with microplastic particles. We examined spheroids composed of fibroblasts, THP-1-derived macrophages, and six different lung cancer cell lines. Spheroids were assessed for viability, proliferation, surface morphology, regional cell distribution, and Young’s modulus (YM). Finally, interactions between spheroids and microplastic particles were investigated under static and dynamic exposure conditions. Morphology and cell segregation differed among spheroids, and we observed significant differences in YM. We found correlations between spheroid YM and lung cancer cell doubling times, between YM measured in the presence and absence of microplastic particles, and between spheroid sizes with and without THP-1 macrophages. Uptake of microplastic particles under dynamic conditions was low, and no clear relationship with YM was apparent. Determination of YM proved to be a useful additional parameter for characterizing cancer spheroids; however, more quantitative methods for measuring particle uptake are needed to define the role of YM in particle–spheroid interactions.</p>