PMC8544124_01
Heterogeneous morphology, MMR protein expression and PD-L1 expression patterns of the 2 synchronous rectal tumours (masses A and B) in the LS patient. (A and G) HE staining of masses A and B showing the classic protruding pattern of adenocarcinoma growth. The IHC staining of mass A showed intact expression of MLH1 (B), PMS2 (C), MSH2 (D), and PD-L1 (F) in addition to loss of expression of MSH6 (E). Mass #B showed intact expression of MLH1 (H), PMS2 (I), MSH2 (J), MSH6 (K) and PD-L1 (L). All images were collected at 100x magnification.
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Mass A demonstrated deficient MMR (dMMR); specifically, there was an absence of MSH6 protein but normal expression of MLH1, MSH2 and PMS2. Mass B expressed all 4 MMR proteins and was therefore deemed to have proficient MMR (pMMR) (Figure 1). Mass B presented strong positive PD-L1 expression; however, it had less than 1% positivity for tumour cells and 5% positivity for immune cells (Figure 1).
The patient's pedigree. The proband had rectal cancer and carried the MSH6 p.R495* germline mutation. Similarly, the individuals (the patient's mother and the patient's brother) without cancers carried the MSH6 p.R495* germline mutation. One of the patient's uncles had colon cancer but did not undergo NGS assessment.
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In addition, one of the patient's uncles was affected by colon cancer without detailed information (Figure 2).
Assessment of the TIME via multiplex IHC (mIHC). (A and F) The green fluorescence indicates CD8+ T cells. (B and G) The pink fluorescence indicates PD-1 expression. (C and H) The yellow fluorescence indicates CD68 expression. (D and I) The Orange fluorescence indicates PD-L1 expression. (E and J) The pictures show all layers merged.
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In particular, the CD8+ T cell proportions in the two CRC tumours were 9.07% and 6.63%, respectively (Figure 3). CD8+PD-1+ T cells and CD68+PD-L1+ macrophages (Figure 3). The HLA-I molecules were of the hla-b44 supertype, which are positive indicators for immunotherapy. Considering the numerous markers indicating the potential of immunotherapy, including MSI-H, high TMB, presence of CD8+PD-L1+ cells and CD68+PD-L1+ macrophages, and the HLA-b44 supertype, ICI strategies had the potential to be effective.