The association between Hairy Cell Leukemia (HCL) and non-tuberculous mycobacterial infections (NTMs) is well described, most notably Mycobacterium kansasii. The exact pathophysiology is not known. We report a case of a 31-year-old male with concomitantly diagnosed HCL and disseminated M kansasii infection who presented with rash, pancytopenia, and bulky axillary lymphadenopathy. The M kansasii was initially diagnosed through use of cell-free DNA detection and confirmed by bone marrow and lymph node cultures. Hairy Cell Leukemia was diagnosed with peripheral flow cytometry and confirmed via the same bone marrow sample. His HCL was put into remission with a single course of cladribine and rituximab chemotherapy; however, his M kansasii infection persisted for 6 months despite aggressive antimicrobial and surgical therapy. It was finally controlled using high-dose rifampin in combination with azithromycin and ethambutol. This case highlights the known link between HCL and M kansasii. Furthermore, it hints at potential causes beyond chemotherapy-induced immunocompromise. Notable possibilities include HCL cells acting as sanctuary sites for M kansasii to evade the immune system, and subclinical M kansasii infections causing NLRP3 inflammasome overactivation to trigger the oncogenic transformation to HCL. More research into the pathophysiologic link between HCL and M kansasii infections would allow for more effective prevention, diagnosis, and treatment of these severe atypical infections which are the major cause of morbidity in the cladribine era of HCL treatment.

Concern has emerged about the prevalence of second cancers among patients with hairy cell leukemia (HCL) treated with purine analogs. We investigated 513 patients with HCL treated with cladribine over the last 30 years at 18 Italian centers and calculated their standardized incidence ratios (SIRs). We identified 24 patients with a second cancer diagnosed at a median time from treatment with cladribine of 59.9 months (range: 9.2-169.7 months). All patients with solid neoplasms presented with a limited-stage disease, except four cases of locally advanced cancer; multiple myeloma patients had a smoldering disease, while lymphoma patients had stage Ie and stage IV diseases. Response to therapy was complete in 19 cases; 1 patient is still receiving treatment for a relapsing bladder disease, while 2 patients progressed during treatment and died. These two patients died from unrelated causes: one from infection and one due to surgery complications. The median OS from HCL was 98.5 months (range: 38.4-409.2 months), while the median OS from second cancer was 27.6 months (range: 1-117.8 months). The SIR was 0.86 (95% CI: 0.54-1.30) for males and 1.13 (95% CI: 0.36-2.73) for females: no statistically significant differences were highlighted. We were not able to demonstrate an excess of second cancer or a significant association with the specific studied neoplasm.

Hairy cell leukemia (HCL) is a rare lymphoproliferative disorder classically presenting with cytopenia and recurrent infections but atypical manifestations such as bone lesions, skin lesions and effusion have been described. We report here an unusual meningeal localization in a 33 years old man who presented with headache, hand paresthesia and visual symptoms. Brain magnetic resonance imaging revealed an occipital meningeal lesion. Diagnostic explorations led to the diagnosis of classical HCL with meningeal localization. After treatment by cladribine and rituximab the patient rapidly improved and is still in complete remission 12 months after end of treatment. The literature review identified 9 other cases of HCL with central nervous system localization (CNS) presenting with brain parenchyma and/or meninges localization. Four out of 9 patients presented with hyperleukocytosis. Most patients experienced good responses with various treatments. Cladribine alone or with rituximab led to complete responses similar to our patient. In our patient, molecular biology revealed KLF2 mutations, which implication in the atypical localization could be suspected but would need dedicated studies. In conclusion, CNS localizations of HCL are rare but can be observed and treatment with cladribine alone or with rituximab appears as an effective strategy.

Hairy cell leukemia (HCL) is an indolent B-cell lymphoma characterized by a specific genetic mutation, BRAF V600E, which affects the specific morphology and oncogenesis. For HCL, few reports regarding secondary central nervous system involvement (SCNSI) are available. Herein, we present the case of an 80-year-old woman who had a relapse of HCL with SCNSI.
The diagnosis of HCL was made in June 2015 after identifying BRAF V600E proteins by immunohistochemical analysis, and the disease was then controlled for 6 years by employing chemoimmunotherapy. In February 2021, the patient was admitted with neurological symptoms such as dizziness. Magnetic resonance imaging of the brain showed abnormal enhancement in the cerebrum, and cerebrospinal fluid analysis revealed neoplastic cells without transformation into large cells. Thus, the patient was diagnosed as having SCNSI in HCL.
We report a case of a rare clinical presentation of SCNSI in HCL with literature review.

Hairy cell leukemia (HCL) is a rare malignancy that primarily affects the bone marrow, peripheral blood, and spleen. The most common presenting features of HCL are splenomegaly or cytopenias causing fatigue, infections, or hemorrhagic manifestations. Symptoms involving the soft tissue or bone are rare. HCL can rarely present with immune-mediated polyarthritis. This presentation can be confused for other pathological entities, such as Felty\'s syndrome, and can be differentiated from this with bone marrow biopsy. This case report looks into a rare presentation of HCL in which transient polyarthritis of the knees was the presenting symptom.

A 49-year-old male patient who had been diagnosed with variable hairy cell leukemia (HCL-V) was treated with interferon for half a year but exert no obvious effect. After two courses of chemotherapy with cladribine, he achieved remission, and splenomegaly significantly improved (the length in craniocaudal dimension decreased from 15.8cm to 11.8cm). Four years later, the patient got disease relapse and was recommended for another cycle of cladribine (6mg for 7 days). On the last day of cladribine, the patient developed fever with needle-like red rashes on the face, limbs, and trunk. At the very beginning, the rash was lighter in color, sparsely distributed, and without obvious itching. Three days later, the rash gradually darkened, expanded and merged, with itching. With the application of high dose gamma globulin and corticosteroids (prednisolone combined with dexamethasone), the rash finally faded, and the patient was discharged. Rash caused by cladribine is not uncommon, such serious and widespread drug-induced rash is rare, and there are few reports. This article reviewed relevant studies and treatments.

BACKGROUND: Hematologic diseases are rarely present with sudden hearing loss as an initial symptom. Although the precise cause of sudden sensorineural hearing loss has not been identified, several pathophysiological mechanisms have been proposed. However, a variety of hematologic diseases are among the causes of sudden onset deafness. This article represents the first reported case of Hairy cell leukemia (HCL) which presented with acute unilateral profound sensorineural hearing loss as an inital mainfestation.
METHODS: A 41-year-old man presented with unilateral sudden hearing loss for one day\'s duration was found to have HCL during a worked up for his hearing loss. The disease worsened, and there was no improvement in his hearing.
CONCLUSIONS: Sudden sensorineural hearing loss can rarely be seen as a paraneoplastic occurrence.Very few cases have been reported in the literature. It has been reported as a presenting symptom of leukemia in numerous clinical and histopathological reports concerning the hearing loss in hematologic diseases. Our case is an example of such a rare incidence.
CONCLUSIONS: The purpose of this study is to draw physicians\' attention to the possible association between acute sensorineural hearing loss to HCL, and to highlights permanent deafness as a complication secondary to HCL. Furthermore, it is important to increase awareness on early diagnosis and treatment that may improve treatment outcomes.

Treatment of hairy cell leukemia (HCL) with alfa-interferon and purine analogs significantly prolongs survival in these patients. However, with life prolongation, an increased risk of secondary malignancies has been reported. Acute myeloid leukemia (AML), as a second malignancy after HCL treatment is extremely rare and has been reported in only 12 cases so far. We here report additional 2 cases of CD56+ AML developed after sustained clinical remission of HCL achieved with cladribine (2 and 6 years after, respectively). The first patient refused chemotherapy and shortly thereafter died. The second patient responded to chemotherapy and was successfully allo-transplanted. Three years later, the patient is in stable clinical remission, which is a unique case in the literature. In conclusion, it is not clear whether development of AML in HCL patients is caused by mutagenic potential of the applied chemotherapy or by immune suppression/ perturbations as a characteristic of the underlying disease.

Hairy cell leukemia (HCL) is a rare mature B cell leukemia. Purine analogs are the mainstay of treatment of HCL, but relapse after purine analog therapy is common. Outcomes of treatment of relapsed/refractory HCL typically diminish with each successive line of therapy. Moxetumomab pasudotox-tdfk is a novel recombinant immunotoxin approved for the treatment of patients with relapsed/refractory HCL who have received at least two prior therapies, including a purine analog. This article reviews HCL treatment, focusing on moxetumomab pasudotox-tdfk, its place in therapy, considerations for preparation and administration, and strategies for prevention and management of toxicities.
A literature search was conducted in the PubMed database from inception to January 2019, using the following terms: moxetumomab, hairy cell leukemia, relapsed/refractory hairy cell leukemia, immunotoxin, and CD22. The package insert and available posters and abstracts were also reviewed.
FDA approval of moxetumomab pasudotox-tdfk was based on a phase III single-arm, open-label trial in 80 patients. Treatment with moxetumomab pasudotox-tdfk yielded a durable complete response rate of 30% with a median duration of response that had not yet been reached at a median follow-up of 16.7 months. The objective response rate was 75% based on blinded independent central review. The most common adverse reactions were infusion-related reactions, edema, nausea, fatigue, headache, pyrexia and anemia. Serious adverse events include capillary leak syndrome and hemolytic uremic syndrome.
Clinicians providing care for patients receiving moxetumomab pasudotox-tdfk should be aware of the strategies required for safe administration, including the management of serious adverse events.

BACKGROUND: Concurrent hairy cell leukemia (HCL) and chronic lymphocytic leukemia (CLL) is rare; management is inadequately described in the literature.
METHODS: Retrospective chart review and clinical follow-up.
RESULTS: Five patients are described. The first patient developed synchronous HCL and CLL and was treated with rituximab for 13 months with HCL in remission and stable CLL. The second patient developed HCL and was treated with cladribine. His disease recurred 7 years later which was retreated with cladribine. Seven years later, he developed asymptomatic CLL. The third patient developed CLL, managed expectantly, then developed HCL 10 months later, and was treated with cladribine. Although his HCL went into remission, there was a slow redevelopment of CLL for which expectant management was done. The fourth patient developed concurrent CLL and HCL, received cladribine, with subsequent development of worsening abdominal lymphadenopathy and was lost to follow-up. The last patient developed concurrent HCL and CLL and was also diagnosed with lung adenocarcinoma; this patient was also lost to follow-up.
CONCLUSIONS: The development of concurrent HCL and CLL may indicate a common origin. Patients with HCL may subsequently develop CLL, thus mimicking a relapse of HCL. Therapy requires individualized approach including watchful waiting in asymptomatic cases. Rituximab may be useful to treat both disorders simultaneously.