Ο καρκίνος χρειάζεται θεραπεία.

In Greek, nouns often appear with the definite article much more often than in English. So ο καρκίνος is literally the cancer, but in many contexts it is simply the normal Greek way to talk about cancer.

Here, ο is:

• masculine
• singular
• nominative

It matches καρκίνος, which is a masculine singular noun.

It can often mean either one, depending on context.

In this sentence, Ο καρκίνος χρειάζεται θεραπεία, Greek can use the article even when speaking generally, so it may correspond to English Cancer needs treatment.

But in another context, it could also mean The cancer needs treatment, referring to a particular case already being discussed.

So the article does not always make it as specific as English the does.

Because Greek often leaves out the article with an object when it means something general or indefinite.

So θεραπεία here means:

• treatment
• not necessarily the treatment
• not necessarily a treatment in the strongly countable English sense

It is a general object: cancer needs treatment.

If you said τη θεραπεία, that would sound more like the treatment, referring to a specific treatment already known from context.

Χρειάζεται means needs or is in need of.

It comes from the verb χρειάζομαι, which means to need.

So:

• χρειάζομαι = I need
• χρειάζεται = he/she/it needs

Even though the dictionary form ends in -ομαι, it has an active meaning. This is very common in Modern Greek: some verbs have middle/passive-looking forms but active meanings.

Because χρειάζεται is the third person singular form of χρειάζομαι.

The subject is ο καρκίνος, which is singular, so the verb must also be singular:

• ο καρκίνος χρειάζεται = cancer needs

The ending -εται is typical for many verbs whose basic form ends in -ομαι.

• ο καρκίνος is in the nominative case because it is the subject of the sentence.
• θεραπεία is in the accusative case because it is the direct object of χρειάζεται.

So the structure is:

• Subject: ο καρκίνος
• Verb: χρειάζεται
• Object: θεραπεία

This is very similar to English word order here.

That is normal for many feminine nouns in Greek. Some feminine nouns have the same form in nominative and accusative singular.

For θεραπεία:

• nominative singular: η θεραπεία
• accusative singular: τη θεραπεία

Without the article, the noun itself stays θεραπεία, so you understand the case from its role in the sentence.

Since it is the thing that is needed, it is functioning as the object, so it is accusative.

A simple pronunciation guide is:

O karkínos chreiázetai therapeía

Main stress:

• καρκίνος → karKÍnos
• χρειάζεται → chreiÁzetai
• θεραπεία → therapeÍa

A few helpful notes:

• χ is not like English ch in chair. It is a rough sound, like the h in huge for some speakers, or like German ich/ach depending on the vowel around it.
• ει in χρειάζεται sounds like ee.
• Greek stress marks are important and should be learned with the word.

Yes. Greek word order is more flexible than English.

The neutral order here is:

Ο καρκίνος χρειάζεται θεραπεία.

But Greek could change the order for emphasis, for example:

• Θεραπεία χρειάζεται ο καρκίνος. = It is treatment that cancer needs.

That said, the original version is the most straightforward and natural for a learner to use.

Greek often does omit subject pronouns like he, she, or it, because the verb ending already shows the person and number.

But ο καρκίνος is not a pronoun; it is the full noun subject. If you want to say what needs treatment, you normally include it.

You could not simply say Χρειάζεται θεραπεία unless the subject were already understood from context, in which case it would mean something like:

• He/She/It needs treatment
• or Treatment is needed, depending on context

So including ο καρκίνος makes the sentence clear and complete.

Yes. Καρκίνος is a masculine noun, so it takes masculine forms like:

• ο καρκίνος = nominative singular
• τον καρκίνο = accusative singular

Its gender is grammatical, so adjectives and articles referring to it must agree with it.

Yes, but χρειάζεται is a very natural and standard choice for needs.

For example, Greek sometimes also uses:

• θέλει in more informal speech, literally wants, but often meaning needs in context

So you may hear:

• Ο καρκίνος θέλει θεραπεία.

That can sound more colloquial.
Ο καρκίνος χρειάζεται θεραπεία is a clear, standard, and safe form for learners.