Although aplastic anemia (AA) and myelodysplastic syndrome (MDS) are separate entities with different management, distinction between the two can be difficult on morphological basis due to hypocellularity of bone marrow. MDS is one of the serious complications of AA. Karyotyping is definitive in the diagnosis of MDS. Better and robust investigations like F-18-Fluoro-deoxy-Glucose Positron Emission Tomography/Computed Tomography (F-18-FDG PET-CT) are essential in high risk patients with haematological malignancies and in those relapsing within a short period of time after initiation of therapy or having refractory disease. It might be helpful in the development of individual treatment algorithms for these high-risk patients. There may be unique problems in hematological malignancies where the transformation of one pathology into another may be silent with no biomarkers that can predict this transformation e.g. transformation of MDS from AA. Studies have shown that immune suppression can lead to a variety of haematological and lymphoproliferative disorders which may co-exist. F-18-FDG PET-CT may be useful in identifying the primary or occult sites of malignancy and also can direct the site from which biopsy can be attempted. We present a patient with Carcinoma right breast who developed hematological and lymphoproliferative disorders during the course of her treatment. In this case, AA transformed to MDS with abnormal karyotype (chromosome 9 mutation) and then progressed further to manifest cutaneous T cell lymphoma before patient succumbed to her illness. Immune mediated suppression of haemopoiesis has been considered the most important mechanism in this case.