Structural and Complex Chromosomal Aberrations Frequently Develop in Skin Fibroblasts after Allogeneic Stem Cell Transplantation.

Radiotherapy and chemotherapy are known to be mutagenic and may cause cytogenetic aberrations. Secondary neoplasms, which also arise after hematopoietic stem cell transplantation, are frequently associated with cytogenetic aberrations, which might be caused by DNA-alterations due to radio- and chemotherapy.

Skin samples were examined for cytogenetic aberrations in patients after allogeneic stem cell transplantation (SCT). In a retrospective study skin samples were taken and examined from 18 patients 23–216 months (range 38 months) after allogeneic SCT. Underlying diagnoses were ALL (3 pts), AML (4 pts), CML (10 pts), MDS (2 pts), NHL (1 pt).

In a prospective trial 20 pts were included. Skin biopsies were taken before conditioning, then at 3–6 months as well as 12 months after SCT. Median age before SCT was 32 years (range 16–49). Underlying diagnoses were ALL (4 pts), AML (3 pts), CML (7 pts), other CMPS (2 pts), MDS (3 pts), NHL (1 pt).

Samples from all patients were cut into small pieces, placed at the bottom of three culture flasks and fibroblasts cultured according to standard techniques. Cytogenetic analysis was performed with trypsin-Giemsa banding technique. The number of cells with aberrant karyotypes, the number of clonal chromosome abnormalities, the number of breakpoints per aberrant metaphase, the preferential location of breakpoints in chromosome bands and the type of chromosomal lesions (e.g. translocations, deletions, duplications) were determined.

In retrospective analysis, all 17 evaluable patients had cytogenetic aberrations, comprising 33–100% cells per patient. Aberrant cells had a median of 4 breakpoints per aberrant metaphase.

In the prospective study, evaluable samples from 18 patients before SCT could be analysed and only 2/18 revealed cytogenetic aberrations.

3–6 months after allogeneic SCT, abnormal karyotypes were detected in 12/13 patients. 47–100% of analysed skin cells per patient had aberrant karyotypes (median 77%). Aberrant metaphases had 1–10 chromosomal breakpoints (median 3). 12 months after allogeneic SCT, all 11 evaluable skin samples demonstrated aberrant karyotypes, the number of abnormal cells being between 33–100% (median 63%). 2–5 clones were detected per patient. 1–9 breakpoints were found per aberrant metaphase.

All chromosomal aberrations were structural (translocations, deletions, additions, inversion), most of them were balanced translocations; some aberrations were complex.

The number of aberrant cells differed significantly before SCT on one hand and both time points after SCT (p<0.01) on the other hand, but not between the two timepoints after SCT (p=0.237).

In univariate analysis, only acute leukemias (p=0.028) had a significant impact on chromosomal aberrations detected. 40–65 months after allogeneic SCT, none of the patients in the prospective study had developed secondary neoplasms and no carcinomas of the skin were detected. 1 patient in retrospective analysis had developed breast cancer 216 months after allogeneic SCT.

In conclusion: Cytogenetic aberrations are very frequently induced in skin fibroblasts after TBI and high-dose chemotherapy in pts receiving allogeneic SCT. Aberrations persist and remain stable for prolonged periods after allogeneic SCT. The clinical implication of this finding needs longer follow-up.