Thyroid nodules (TN), hyperplasia of the mammary gland (HMG), uterine leiomyomas (UL), and benign breast nodules (BN) frequently occur either simultaneously or sequentially, leading to multisystem disease presentations that have garnered significant scholarly attention. It has been reported that patients with UL have a 38.7% likelihood of developing TN, compared to just 20% in the general population, suggesting that UL may elevate the risk of TN (1). Additionally, patients with BN are more prone to concomitant TN, and vice versa, indicating a bidirectional pathogenic relationship between BN and TN (2). Some researchers refer to TN, HMG, and UL as the “female triad,” implying that the presence of nodules, hyperplasia, or masses in any one of these organs (thyroid, breast, or uterus) in female patients often correlates with accompanying symptoms in the other two. This points to shared causative factors and pathogenic mechanisms among these diseases (3). Recent studies have revealed that patients with Hashimoto’s thyroiditis (HT) frequently present with multiple comorbidities (4, 5), with TN co-occurrence rates as high as 24.3% (6) and cancer complication rates reaching 58.3% (7–9). In clinical practice, it is common for patients with HT to be diagnosed with various systemic diseases; however, the specific comorbidities, influencing factors, and underlying pathogenesis remain unclear. Therefore, this study aims to explore the comorbidity patterns, related influencing factors, and potential pathogenesis in patients with HT, thereby offering valuable insights for clinical diagnosis and treatment.

Among the 429 patients with HT, 348 presented with comorbidities, resulting in a prevalence rate of 81.19%. Eight types of comorbidities were identified, with TN, HMG, UL, and BN being the most prevalent, accounting for 53.1%, 24.9%, 24.2%, and 23.5% of cases, respectively. Association rule analysis revealed that TN was central to the binary comorbidity pattern, while TN and HMG formed the core of the ternary pattern, and TN, HMG, and UL were central to the quaternary pattern. These findings highlight the high prevalence of comorbidities in patients with HT and emphasize the need to explore contributing factors and potential pathogenesis.

Regarding influencing factors, univariate analysis identified sex, age, marital status, TPOAb/TGAb antibody status, and L-T4 treatment history as significant correlates of HT comorbidity. Multivariate logistic regression further confirmed that sex, age, and L-T4 treatment history were independently associated with HT comorbidity. Specifically, the likelihood of comorbidities was significantly higher in women and older patients with HT. Female patients with HT were found to be 6.242 times more likely to have comorbidities than their male counterparts, potentially due to greater variability in estrogen levels (11). Estrogen receptors are present in the tissues of the thyroid, breast, and uterus, suggesting that fluctuations in estrogen may play a significant role in the development of comorbidities in female patients with HT (12–14). Previous studies have also linked increasing age with the incidence of nodular disorders (15), a finding consistent with our results.

Interestingly, patients with HT undergoing L-T4 therapy had a lower likelihood of developing TN, breast hyperplasia, mammary nodules, and uterine fibroids. This could be attributed to L-T4 treatment correcting the hypothyroid state and the associated endocrine and metabolic disturbances. Patients with HT often experience hypothyroidism, which leads to elevated TSH levels that can stimulate thyroid tissue hyperplasia and nodule formation, increasing the risk of benign TN (16). L-T4 therapy helps normalize thyroid hormone levels and reduce TSH, thereby decreasing overstimulation of thyroid follicular cells, lowering the risk of hyperplasia and nodules, and potentially causing existing nodules to regress (17–20).

Additionally, thyroid hormone levels interact with estrogen (21, 22), and chronic exposure to elevated estrogen has been linked to a higher susceptibility to hypothyroidism (23). High estrogen levels can also influence the normal development of the mammary glands and uterus (24). Furthermore, metabolic disorders such as insulin resistance, lipid metabolism disturbances, and chronic inflammation—often associated with hypothyroidism—may indirectly affect cell proliferation and increase tumor risk (25).

PPI network analysis identified AKT1, TP53, EGFR, INS, and TNF as potential core targets for comorbidities in patients with HT. To determine whether these targets were abnormally expressed in patients with HT, GEO data (GSE138198), which profile mRNA expression in the thyroid tissues of patients with HT, were analyzed alongside relevant literature. The GEO data revealed the expression of AKT1, TP53, EGFR, and TNF mRNAs in the thyroid tissues of patients with HT, with TP53 showing significantly higher expression (p _adj < 0.05; Supplementary Figure 1 ). Literature reports also confirmed that TP53, which encodes the cellular tumor antigen P53 (P53), is overexpressed in the thyroid gland of patients with HT (26).

In contrast, the GEO data did not show significant differences in the mRNA expression of AKT1, EGFR, TNF, and INS in the thyroid tissues of patients with HT. This may be attributed to factors such as mRNA translation efficiency, post-translational modifications, and external influences on protein expression. Notably, in human normal thyroid cells (Nthy-ori 3-1), phosphorylation of AKT (p-AKT) is significantly upregulated in response to IL-23 stimulation, a cytokine known to be elevated in patients with HT (27). EGFR expression has also been reported to be elevated in the thyroid tissues of patients with HT (28). INS, secreted by pancreatic islet cells, often accompanies an increase in insulin secretion in patients with HT (29). Furthermore, TNF-α is significantly elevated in the serum of patients with HT (30). Thus, AKT1, EGFR, TNF, and INS demonstrate characteristically high expression in the thyroid tissues, cells, or peripheral blood of patients with HT.

Mechanistically, AKT1 is a critical component of the PI3K/Akt signaling pathway, which plays a vital role in cell proliferation, survival, and metabolism (31). Activated AKT promotes the survival and proliferation of thyroid follicular epithelial cells, breast ductal epithelial cells, and uterine smooth muscle cells, inhibits apoptosis, and supports the formation of nodules and leiomyomas (32–34). High expression of AKT or p-AKT has been linked to the development of TN, HMG, and UL (35–37). TP53, a well-known tumor suppressor gene, is frequently mutated in various cancers, including breast and thyroid cancers (38). Literature indicates that TP53 is also overexpressed in benign TN, HMG, and UL (26, 39, 40). EGF stimulates cell proliferation by binding to its receptor EGFR, which activates downstream MAPK and PI3K-Akt signaling pathways (41). Recent studies have demonstrated that EGFR signaling intersects extensively with inflammatory factor signaling, creating a positive feedback loop that amplifies both pro-proliferative and pro-inflammatory signals (42). Elevated EGFR expression levels have been observed in the diseased tissues of patients with both benign and malignant TN (43), where it promotes abnormal breast tissue proliferation (44) and UL development (45)INS, a major regulator of glucose metabolism, also has potent mitogenic and anti-apoptotic effects. By activating the PI3K/Akt pathway through the insulin receptor, it regulates cell metabolism and growth (46). Both TN and UL have been associated with insulin resistance, although the relationship between HMG and INS remains unclear (47–49). TNF, a pro-inflammatory cytokine, activates the PI3K/Akt pathway and exacerbates immune-inflammatory responses (50). High TNF expression has been reported in TN, HMG, and UL.

This study focused on the comorbidity patterns and potential mechanisms in patients with HT, integrating clinical data, statistical modeling, network pharmacology, and pathway enrichment analysis. The findings suggest that the TN–HMG–UL triad constitutes the core comorbidity cluster in HT. Being a woman and increasing age are associated with a higher likelihood of comorbidities, while L-T4 administration is linked to a decreased likelihood. AKT1, TP53, EGFR, INS, TNF, and the PI3K–Akt signaling pathway were identified as potential molecular foundations for HT-related co-morbidities.

Notably, this study employed a cross-sectional design, which allows for the identification of clinical epidemiological characteristics related to HT comorbidities but does not establish causal relationships. Further verification through multicenter, large-sample cohort studies is necessary. Additionally, network pharmacology was used to predict potential core targets of HT-related comorbidities. Preliminary support for the actual expression of these targets in the tissues of patients with HT was provided by the GEO database and relevant literature. However, due to the study’s limitations, only literature cross-references were used to support the functional relevance of these targets. Future clinical validations—such as HT co-morbidomics—are required to provide direct evidence for the prevention, diagnosis, and treatment of the disease.