Adult T-cell leukemia/lymphoma (ATLL) is an aggressive mature peripheral T-cell neoplasm caused by the Human T-cell Lymphotropic Virus Type 1 (HTLV-1). An estimated 10 to 20 million individuals are infected with HTLV-1 worldwide [1], most of them in endemic regions for the virus, such as southwestern Japan, the Caribbean, intertropical Africa, the Middle East, and South America [1], [2], [3], [4], [5].

Most HTLV-1 infected people are carriers who remain asymptomatic throughout their life. The estimated lifetime risk of developing ATLL among infected patients is 2.5 to 4% and the latency period usually varies from three to five decades after infection [6]. Once the disease is established, ATLL is classified according to the extent of organ involvement, circulating neoplastic cells in peripheral blood, serum lactate dehydrogenase (LDH) and serum calcium levels. Four clinical subtypes of ATLL are recognized: acute, lymphomatous, chronic, and smoldering [7]. The acute and lymphomatous subtypes are considered aggressive forms and usually present with leukocytosis, circulating lymphoma cells, elevated serum LDH, hypercalcemia, generalized lymphadenopathy, hepatosplenomegaly, and bone marrow involvement. Due to the frequent immunodeficiency state and high rate of opportunistic infections, these patients have a poor prognosis, with a median survival of less than 1 year. The chronic and smoldering subtypes have a more indolent clinical course with low or high numbers of circulating lymphoma cells, normal or slightly increased LDH, normal calcium levels, cutaneous or pulmonary lesions, absent or minimal lymphadenopathy or mild hepatosplenomegaly, and no bone marrow involvement. Progression from indolent to aggressive forms occurs in 25% of cases over variable periods of time [1], [2], [3], [4], [5].

Almost any organ system can be involved by ATLL [8]. Cardiac involvement by ATLL is rarely reported and, when apparent, it is usually seen in patients with aggressive ATLL subtypes [9], [10], [11], [12], [13], [14], [15], [16], [17]. However, isolated involvement of cardiac valves is extremely rare, with only three cases reported to date [9,[18], [19], [20]]. Herein, we report a patient presenting with congestive heart failure due to mitral valve regurgitation that prompted cardiac valve replacement, which ultimately showed ATLL infiltration confined to the mitral valve.