European Journal of Cardiovascular Medicine

Breast cancer is the most commonly diagnosed malignancy among women worldwide and remains a leading cause of cancer-related mortality [1]. Despite advances in screening and treatment, breast cancer continues to exhibit heterogeneity in terms of clinical presentation, prognosis, and response to therapy [2]. Over the past two decades, molecular classification of breast cancer has emerged as a crucial tool for guiding personalized treatment and predicting outcomes. The molecular subtypes are primarily defined based on the expression of hormone receptors (estrogen receptor [ER] and progesterone receptor [PR]), human epidermal growth factor receptor 2 (HER2/Neu), and the proliferation marker Ki-67 [3].

Immunohistochemistry (IHC) has become the standard method for determining these molecular subtypes in routine clinical practice, providing a cost-effective and widely available alternative to gene expression profiling [4]. The major IHC-based molecular subtypes include Luminal A, Luminal B, HER2-enriched, and Triple Negative Breast Cancer (TNBC), each associated with distinct clinical behaviors and prognostic outcomes [5]. Luminal A tumors are typically ER-positive, PR-high, HER2-negative, and show low proliferative activity, generally associated with favorable prognosis [6]. Luminal B tumors are also ER-positive but exhibit higher proliferation rates or HER2 positivity, correlating with an intermediate prognosis [7]. HER2-enriched tumors lack hormone receptor expression but overexpress HER2, often associated with aggressive disease [8]. TNBC tumors are negative for ER, PR, and HER2 and are frequently linked with poor clinical outcomes due to limited targeted therapy options [9].

Molecular subtyping is not only predictive of disease prognosis but also plays a pivotal role in therapeutic decision-making, particularly regarding the use of neo-adjuvant chemotherapy and targeted therapies [10]. Several studies have demonstrated significant associations between molecular subtypes and rates of recurrence, overall survival, and treatment response, underscoring the importance of subtype-specific management strategies [11,12]. In India, breast cancer incidence is rising, yet data on clinical outcomes based on molecular subtyping, particularly from tertiary care centres in North Kerala, remain limited. Therefore, this study aimed to evaluate the clinical outcomes and recurrence patterns of breast cancer patients stratified by IHC-based molecular subtypes in a tertiary care centre in North Kerala.

Study Design

This was a record-based retrospective study conducted to assess the clinical outcome and recurrence pattern of breast carcinoma patients based on molecular subtyping using immunohistochemistry (IHC).

Study Setting

The study was carried out in the Department of Pathology, MES Medical College, Perinthalmanna, in collaboration with the Department of Oncology of the same tertiary care centre located in North Kerala.

Study Period

The study was conducted from 1st January 2021 to 1st July 2022.

Study Population

The study population comprised patients diagnosed and treated for breast carcinoma after molecular subtyping by IHC between 1st January 2015 and 1st January 2018 at the Department of Pathology and Oncology, MES Medical College. Each case was followed up for a period of three years to assess disease outcome and recurrence.

Inclusion Criteria

• Female patients diagnosed and treated for breast carcinoma after molecular subtyping by IHC, including ER, PR, HER2/Neu, and Ki-67 markers.
• Patients who had completed the full course of treatment and provided consent for follow-up.

Exclusion Criteria

1. Incomplete case records.
2. Deaths due to causes other than breast cancer.
3. Patients with secondary malignancies other than breast cancer.
4. Patients who did not provide consent for follow-up.
5. Cases that could not be followed up during the study period.

Sample Size Determination

The sample size was calculated using the formula:

Where,

• (standard normal variate at 95% confidence interval),
• (prevalence of recurrence as per previous studies),
• (absolute error).

Based on this calculation, the required sample size was 52 cases.

Working Definitions

The clinical outcome was assessed using parameters such as age, menopausal status, tumour laterality, initial stage, and IHC molecular subtypes.
Event-free survival was defined as the time from completion of treatment to the occurrence of any adverse event (relapse or death related to disease).

The molecular subtypes were defined as follows:

• Luminal A: ER+ and/or PR high, HER2−, Ki-67 < 20%
• Luminal B: ER+ and/or PR low, HER2−, Ki-67 > 20% or ER+ and/or PR+ and HER2+
• HER2 Enriched: ER−, PR−, HER2+
• Triple Negative (TNBC): ER−, PR−, HER2−

All patient identities were kept confidential.

Data Collection

After obtaining institutional permission from the Medical Superintendent, breast case records from January 1, 2015, to January 1, 2018, were retrieved from the hospital archives. Data were extracted using a pre-designed questionnaire covering baseline demographic characteristics, comorbidities, IHC subtypes, and event-free survival details.

Follow-up information was obtained by contacting patients telephonically. Consent forms, prepared in the local language, were sent via WhatsApp or email, and follow-up data were recorded upon receiving the signed consent. The sampling technique used was randomised number sampling generated through Microsoft Excel.

Table 1: Age group distribution

The current study divided participants to two groups namely above 40 years and below 40 years. 75.0% (n=51) of the study participants belonged to age group above 40 years.

Table 2: Histological type of the study population

Table 3: Pathological classification of TNM staging

Table 4: COMPARISON OF MOLECULAR SUB-TYPING WITH RECURRENCE

It was observed from the study that IHC subtyping had a statistically significant association with recurrence. The study found that 91.7% of the Luminal type A had incidence of recurrence whereas the recurrence rates for type B, triple negative and Her2neu were 13.3%, 54.5% and 25.0% respectively. The chi-square test for association gave a significant statistical association for this result (p<0.05).

Table 5: COMPARISON OF MOLECULAR SUB-TYPING WITH OUTCOME

On comparing the molecular subtype with neo-adjuvant chemotherapy, it was found that 54.5% of the triple negative expired followed by 50.0% among Her2 neu enriched group. The mortality was lowest among the luminal type A (8.3%). This result didn’t have any statistically significant association. Even if the Luminal A type had higher incidence of recurrence, LN metastasis and margin involvement the rates of mortality were the least among them.

Table 6: COMPARISON OF OUTCOME BETWEEN MOLECULAR SUBTYPE AMONG THOSE WHO TOOK NEO-ADJUVANT CHEMOTHERAPY

The current study found that only 19.0% of those who took neo-adjuvant chemotherapy expired.

On comparing tables 25 and 26 its worth noting that the death rates were higher for those who didn’t took neo-adjuvant chemotherapy compared to that of those who took neo-adjuvant chemotherapy.

Table 7: COMPARISON OF RECURRENCE WITH MOLECULAR SUBTYPE AMONG THOSE DIDN’T TOOK NEO-ADJUVANT CHEMOTHERAPY

The current study found that 48.9% among those who didn’t took neo-adjuvant chemotherapy had incidence of recurrence. Of this ,90.0% of luminal type had recurrence followed by triple negative (62.5%). 33.3% of Her2neu and 16.7% of Luminal type B had also recurrence. This result had significant statistical association.

Breast cancer exhibits significant heterogeneity in terms of clinical behavior, recurrence patterns, and response to therapy, making molecular subtyping crucial for prognostic stratification and therapeutic planning [1,2]. In the present study, 75% of patients were above 40 years of age, which aligns with previous Indian studies reporting a higher incidence of breast cancer among women in the 40–60 years age group [3]. The majority of cases (94.1%) were invasive carcinoma of no special type (NST), consistent with global data indicating that invasive ductal carcinoma remains the most common histological subtype [4].

Our study demonstrated a statistically significant association between molecular subtypes and recurrence. Interestingly, Luminal A tumors, despite having the highest incidence of recurrence (91.7%), exhibited the lowest mortality (8.3%). This paradox may reflect the generally indolent nature of Luminal A tumors, their responsiveness to hormone therapy, and slower disease progression compared to other subtypes [5,6]. Triple negative breast cancer (TNBC) showed high recurrence (54.5%) and mortality (45.5%), consistent with previous literature highlighting TNBC as an aggressive subtype with limited targeted treatment options and poor overall prognosis [7,8]. HER2-enriched tumors had moderate recurrence (25%) and mortality (50%), reflecting the impact of HER2-targeted therapies on survival outcomes [9]. Luminal B tumors showed intermediate recurrence and mortality rates, consistent with their higher proliferative index and partial hormone responsiveness [6].

Neo-adjuvant chemotherapy appeared to improve overall survival in this cohort. Among patients who received neo-adjuvant chemotherapy, only 19% expired, while mortality was higher among those who did not receive it. This suggests that early systemic therapy may reduce disease progression and mortality, particularly in aggressive subtypes such as TNBC and HER2-enriched tumors [10,11]. The findings emphasize the importance of molecular subtyping not only in prognostic stratification but also in guiding treatment decisions, including the judicious use of neo-adjuvant chemotherapy [12].

Despite the strengths of this study, including three-year follow-up and subtype-based stratification, several limitations exist. Being a retrospective study, it is subject to biases such as incomplete data and loss to follow-up. Additionally, the relatively small sample size limits generalizability to broader populations. Nonetheless, the study provides valuable insights into the prognostic significance of IHC-based molecular subtypes in North Kerala, highlighting the need for larger prospective studies to validate these findings

molecular subtyping using IHC is a reliable predictor of recurrence and survival in breast cancer. Luminal A tumors, although prone to recurrence, demonstrate low mortality, whereas TNBC and HER2-enriched subtypes are associated with poorer outcomes. Neo-adjuvant chemotherapy appears to reduce mortality, emphasizing its role in the management of aggressive subtypes. These findings support the integration of molecular subtyping into routine clinical practice to optimize treatment and follow-up strategies.

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