Microsatellite instability in colon epithelium, buccal mucosa, and secondary tumors after allogeneic HCT. Top panels show representative photographs of tissues that were used for microsatellite analysis. An entire colon section before (A) and after (B) laser-capture microdissection of a crypt, 2 laser-microdissected colon crypts (C), a buccal smear (D), and a secondary squamous cell cancer before (E) and after (F) laser microdissection of a malignant area are shown (hematoxylin/eosin stain). Images were visualized using a Zeiss Axiovert 135 microscope and a C-Apochromat 40 ×/1.2 numeric aperture objective (Carl Zeiss, Jena, Germany). Images were acquired using a Zeiss AxioCam MR and Axioplan 2 imaging software. Images were processed using Adobe Photoshop 6.0 (Adobe Systems, San Jose, CA). Panels G, H, and I show representative electropherograms of PCR microsatellite analysis in colon biopsies, buccal smears, and/or secondary tumors. MSS indicates microsatellite stable; MSI, microsatellite instability; P, patient-specific signals as determined from peripheral blood obtained before transplantation; D, donor-specific alleles; Whole Colon, bands found in the examination of a whole colon section; LCM Colon, bands found in examination of 2 laser-captured microdissected colon crypts; Buccal, bands found in the examination of buccal smears; sec. tumor and LCM mal. area, bands found in the examination of a laser-capture microdissected malignant area of a secondary tumor biopsy; N, negative control (no DNA); d+, day of sampling after transplantation; y-axis, relative fluorescent units; and x-axis, fragment length (base pairs). The analyzed microsatellite marker in each case is given. The asterisks indicate novel bands indicative for MSI. The arrow shows a representative stutter peak.