Dermatomyositis (DM) together with polymyositis and inclusion body myositis belong to a group of acquired skeletal muscle diseases known as idiopathic inflammatory myopathies [
1]. DM is considered an autoimmune disease. It may present with variously expressed clinical signs, the most prominent being characteristic rash and muscle weakness. The skin manifestations include heliotrope rash on the upper eye lids, erythematous rash localized on the face, neck, anterior chest, back, and large joints [
2]. Gottron rash refers to violaceous rash or papules localized typically in metacarpophalangeal, and proximal or distal interphalangeal joints. Together with heliotrope rash, it is considered a specific cutaneous feature of the disease. Proximal muscle weakness usually develops slowly over weeks or months [
3]. DM is associated with presence of specific autoantibodies which are usually divided into myositis specific autoantibodies (including anti-Mi-2, anti-CADM-140, anti-SAE, anti-p155/140 (anti-TIF-1γ), anti-MJ, anti-t-RNA synthetase, and anti-PMS1 antibodies) and myositis associated autoantibodies (including anti-Ro/SSA, anti-U1RNP, anti PM/Scl, and Anti-Ku antibodies) [
4]. Recently, a remarkable association between several antibodies and specific clinical presentations have been found [
5]. The majority of cases are idiopathic. However, in ~15–30 % of adult-onset cases, DM is associated with malignancy. Cancer may occur before, at the same time, or following the diagnosis of DM. DM that develops as a consequence of the tumor presence in the body is classified as paraneoplastic. The mechanism how malignancy induces DM is not clear yet. However, several possible mechanisms have been proposed. It has been demonstrated that some tumors, including breast adenocarcinoma, express high levels of myositis autoantigens [
6]. These antigens can also be found in regenerating myoblasts in affected muscles from myositis patients. It is therefore possible that immune response directed against cancer cells cross-reacts with regenerating muscle cells and could therefore be responsible for the pathogenesis of DM [
6]. The most common tumor types associated with DM include gynecological tumors (mainly ovarian cancer), lung, pancreatic, gastric, colorectal cancer, and non-Hodgkin’s lymphoma [
7]. The most common tumor sites in men are lung, prostate, and stomach. This contrasts with DM in women, which is most frequently associated with tumors of breast, ovary, and uterus [
8]. The spectrum of tumor types varies greatly across different regions. DM in Asian populations is, for example, more frequently associated with a nasopharyngeal cancer [
9]. The first case of DM associated with breast cancer was reported in 1916 [
10]. According to published population-based studies, breast cancer is diagnosed in ~10–20 % of malignancy-associated DM cases [
8].
Triple-negative cancer is an intrinsic subtype of breast cancer. It is defined by the absence of estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth factor receptor 2 (HER2) overexpression and/or gene amplification [
11]. It accounts for 15–20 % of newly diagnosed breast cancer cases [
12]. Typical features include younger age at diagnosis, poorer prognosis, and association with BRCA 1/2 mutations [
12]. No data regarding the incidence of anti-TIF-1γ autoantibodies in triple-negative breast cancer has been published so far.