Background Nannizziopsis is a genus of fungi with several known cases in reptiles of pyogranulomatous infections at cutaneous and musculoskeletal level, of rapid and fatal evolution. There are few cases of this genus described in humans, mainly skin affection but also with visceral abcesses, typically in immunosuppressed patients, with a recent visit to Africa. Case presentation A 45-year-old woman immunosuppressed after renal transplantation and with a recent visit to Nigeria presented with a painless breast abcess, ulceration to the skin and bleeding, and non hematic telorrhea. The mammogram, also completed with an ultrasound scan, showed a polylobulated nodule, BI-RADS 4C. Due to the suspicion of breast cancer, a core needle biopsy was performed and the pathology study showed abundant presence of fungal spores and hyphae. It was identified by genomic amplification of the internal transcription spacer region-2 and a percentage of similarity with sequences of Nannizziopsis obscura from GenBank of 98% was obtained. An empiric treatment with anidulafungin was initiated, and after the surgical resection, it was replaced by isavuconazole, with a total time of treatment of one month. Conclusions This is the first case report of a successful treatment of Nannizziopsis obscura with isavuconazole, with the shortest time of treatment published for this fungi. We highlighted the importance of referring difficult to diagnose species to reference centers, as well as achieving the most complete resection in order to shorten the antibiotic therapy.

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