Spectral karyotyping shows loss of transduced chromosome in relapsed tumor. Spectral karyotyping (SKY analysis) of metaphases from a GCV-sensitive and a GCV-resistant clone. (Ai, Bi) Original RGB (red-green-blue) image after acquisition; (Aii, Bii) inverted DAPI image showing chromosome banding; and (Aiii, Biii) SKY karyotype after chromosome classification. (Aiii) The sensitive cell showed 3 normal chromosomes 19 and a Der(19)T(6B;19D) (arrow); (Biii) the resistant cell revealed 4 normal chromosomes 19 and has thus lost the marker Der(19)T(6B;19D). The complete karyotype is provided in Table 2.