Hypercalcaemia, defined as an abnormally high level of calcium in the blood, can commonly be caused by which of the following?

Introduction / Context:
This question examines your understanding of the major clinical causes of hypercalcaemia, a condition where blood calcium levels are higher than normal. Recognising that malignancy and primary hyperparathyroidism together account for a large proportion of hypercalcaemia cases is important for clinical reasoning. The correct answer reflects this frequent association seen in medical practice.

Given Data / Assumptions:
- Hypercalcaemia is defined as elevated serum calcium.- The options mention malignancy, primary hyperparathyroidism, both together, neither, and an unrelated condition.- You are expected to know common causes rather than rare or exotic ones.- Iron deficiency is included as a distractor condition not typically linked with high calcium.

Concept / Approach:
In adults, the two most frequent causes of significant hypercalcaemia are primary hyperparathyroidism and malignancy. Primary hyperparathyroidism involves overproduction of parathyroid hormone, which increases bone resorption, intestinal absorption and renal reabsorption of calcium. Malignancy may cause hypercalcaemia through bone metastases or secretion of parathyroid hormone related peptides. By contrast, iron deficiency anaemia does not raise calcium levels. Therefore, the correct choice is the option that includes both malignancy and primary hyperparathyroidism as causes.

Step-by-Step Solution:
Step 1: Recall that parathyroid hormone increases blood calcium by acting on bone, kidneys and intestines.Step 2: Recognise that primary hyperparathyroidism represents overactivity of the parathyroid glands and is therefore a classic cause of hypercalcaemia.Step 3: Remember that many cancers, especially those with bone involvement, can lead to high calcium levels, making malignancy another major cause.Step 4: Evaluate each option and identify that option C, which lists both malignancy and primary hyperparathyroidism, matches this clinical knowledge.Step 5: Exclude options that mention neither or unrelated conditions such as iron deficiency.

Verification / Alternative check:
Clinical summaries often state that in adult patients the two most common causes of hypercalcaemia are primary hyperparathyroidism and malignancy.Diagnostic flow charts for elevated calcium levels usually begin by distinguishing between these two groups of causes.This pattern confirms that both A and B are valid causes and that the correct combined choice is option C.

Why Other Options Are Wrong:
Option A alone is incomplete because malignancy is a common cause but not the only major one mentioned in the options.Option B alone is also incomplete because primary hyperparathyroidism is important but malignancy must also be included.Option D is wrong because it denies the role of both malignancy and hyperparathyroidism, which contradicts clinical evidence.Option E is wrong because chronic iron deficiency anaemia does not typically produce high calcium levels and is included purely as a distractor.

Common Pitfalls:
A common error is to choose only one cause, forgetting that multiple major aetiologies can coexist in exam style options.Another pitfall is to confuse conditions associated with bone disease, such as osteoporosis, with those that directly raise serum calcium.Remember that when a combined option correctly includes all the principal causes described in textbooks, it is often the best answer.

Final Answer:
Hypercalcaemia can commonly be caused by both malignancy and primary hyperparathyroidism.